scientific journals and have hence been inaccessible to many who might otherwise desire to study them. Hence the gathering together into one volume of the main points of that argument, together with a discussion of how they have been used in the establishment of that theory and of the present tendencies and possibilities of that theory, is performing a great service not only to those who desire to learn of the theory, but also to the theory itself, since such work must help to show where modification and extension of the theory are possible and desirable.

It was a desire to meet these needs both of the student and of the theory that led Professor Drude to undertake the production. of the work before us. Hence the purpose of the book is to supply a modern text embracing the entire subject of optics, and to make possible a deeper insight into the modern theory of light.

In order to attain this purpose, the author omits most of the older historical references, and gives only those later ones that will prove useful to the reader in finding the more extended discussions in the periodical literature. In fact, the greater part of the book treats of the work done during the last fifteen or twenty

years.

Hence it differs essentially from other treatises, many of which mention only the work done previous to the last fifteen or twenty years. Thus the discussion of the various mechanical theories of light, with their perplexities as to a mechanically incompressible ether and their shrewd and subtile attempts to annihilate the longitudinal vibrations by assumptions that lead to worse complications, give place in this book to a presentation of the electromagnetic theory, to a tracing of that theory in its consequences, and to a discussion of the problems that are now being solved or that ought to be solved in the near future.

In order to give the reader some idea of the nature of the questions discussed, a few of the more interesting ones will be mentioned. In the chapter on physical conditions for image formation the modern method of attacking the problems of spherical and chromatic aberration is discussed. The chapter

on interference contains a presentation of the manner in which interference is used for obtaining high spectroscopic resolution by introducing a great difference of path between the two interfering beams, and discusses the problems of molecular vibrations to which this use of interference leads. The chapter on diffraction takes up not only the regular treatment of the grating, etc., but also goes into the question of resolving power in general, and the limit of resolution of optical instruments. In the chapter on absorbing media the reader learns of the optical properties of the metals and of the relations that have been established and proposed between the optical and electrical constants. The chapter on dispersion is particularly well done. Starting with the assumption that the smallest particles of a body possess natural periods of vibration, Professor Drude shows how these natural periods of the particles are involved with the period impressed upon the body from without and the index of refraction and the dielectric constant in determining when the dispersion is normal and when anomalous. He also shows how from the observed dispersion, together with other optical and electrical constants of a substance, the position of the absorption bands may be calculated. In the chapter on bodies in motion the reader is introduced to the present state of scientific opinion upon the questions: 'Is the ether at rest? Is its state of rest disturbed by the motion of matter through it?' His attention is also called to the points that need further investigation and discussion. The last portion of the book is given up to a presentation of the relations that have been discovered between thermodynamics and optics. Here important questions concerning the efficiency of a source of light and the conversion of other forms of energy into light are discussed. The last chapter takes up the properties of incandescent vapors and gases and presents the electron theory, calculating the probable size of an electron from optical data. This last portion of the book contains descriptions of work and theories that are not discussed extensively in any other English text.

A glance at the list of questions just pre

sented must convince the reader that the topics discussed in the book are not only most interesting, but are also those with which science is to-day grappling. The method of presentation is also forceful, since it gains power and simplicity because of the unifying influence of the great theory that pervades it throughout. By thus giving a coherent treatment of the problems that are in process of solution at the present moment, Professor Drude has produced a book that is bound to have great influence for good upon the science of optics, since it must impress the student that, to use the author's own words, 'optics is not an old worn-out branch of physics, but in it there pulses a new life.'

. In doing this the author has in addition given a valuable hint to writers of texts-for how much greater would be the interest in physical science among the people generally if many of the time-worn, cut-and-dried (particularly dried) discussions that have clung tenaciously to the texts could be rewritten so as to present the subject entirely from the present and future point of view instead of from that of the past? In such a presentation stress would be laid, as Professor Drude has done, not only upon that which had been settled, but also upon that which still remains to be settled; so that the reader would not be tempted, after reading the book, to think that he knows it all, since everything is finally settled and he can and has committed it to memory.

Thus all students of physics owe a debt of gratitude to the author of this 'Theory of Optics,' not only because he has woven together for them the scattered threads of the electromagnetic theory into a web of pleasing and symmetrical pattern, but also because he has, in so doing, shown how to present a scientific subject in such a way that the student is left with a realization of the fact that the science is alive and teeming with future possibilities, instead of with a feeling of disgust at having had thrust upon him the usual glorified and embalmed image of past grandeur-. a corpse fixed in death.

Thus this work impresses us as a very able and original presentation of a difficult sub

Medical Microscopy. By T. E. OERTEL, M.D. Philadelphia, P. Blakiston's Son & Co. 1902. Small 8vo. Pp. 362.

The facts which a working knowledge of microscopy may reveal to aid in diagnosis are so important that the profession demands an acquaintance with this subject which is coming to be recognized more and more as fundamental in medicine.

This small volume is offered in response to a legitimate voice, as the author believes, coming especially from that part of the medical profession which graduated before much instruction was given in the subjects in which the microscope serves so great a purpose.

Naturally the microscope is the first to receive attention. The various parts are named and their functions explained. The terms used in manipulation are defined and some of the phenomena are considered.

The summary of the facts regarding the habitat, pathogenesis, morphology and cultural characteristics of many of the more important pathogenic bacteria will be of much assistance to those unfamiliar with the subject. The following topics are also briefly treated: preparation of tissue, tumors, blood and the various secretions and excretions of the body.

An author is certainly justified in compiling a work upon medical microscopy in order that the rudiments of the somewhat scattered knowledge may be accessible to all, yet, on the other hand, when such a book compiled from works upon subjects which are experiencing such rapid changes and additions reaches the reader, there will be an opportunity to take exceptions to certain portions of it. This

book is unfortunate in this respect. The technique suggested in many cases, doubtless, will not be received with favor by experienced laboratory workers.

Claim to originality is made by the author with respect to the presentation of the subject only. On the whole, the book is written in a style which is clear and concise. Some of the unqualified statements should be modified to meet the prevailing opinion of to-day. To aid in a future edition we should call attention also to the lettering of the diagrams to represent optical phenomena of the microscope, which we believe to be inadequate and confusing.

A book compiled on the plan of this one will do good service in the place to which the author in the preface modestly assigns it: 'It is to the beginner in microscopy, and particularly to him who must work without the personal guidance of a teacher, that the book may prove of value.'

G. FRANKLIN WHITE.

SCIENTIFIC JOURNALS AND ARTICLES. The American Journal of Mathematics for October contains the following articles: 'The Plane Geometry of the Point in Point-Space of Four Dimensions,' by C. J. Keyser; 'On the Functions Representing Distances and Analogous Functions,' by H. F. Blichfeldt; 'Surfaces whose Lines of Curvature in One System are Represented on the Sphere by Great Circles,' by L. P. Eisenhart; 'On the Invariants of a Homogeneous Quadratic Differential Equation of the Second Order,' by D. R. Curtiss; 'Surfaces of Constant Mean Curvature,' by L. P. Eisenhart.

SOCIETIES AND ACADEMIES.
MICHIGAN ORNITHOLOGICAL CLUB.

AFTER a few years of apparent sleep, the Michigan Ornithological Club was reorganized at Detroit on February 13, 1903. The officers elected for the current year are: President, Adolphe B. Covert, Ann Arbor; Vice-President, Dr. Phillip E. Moody, Detroit; Secretary-Treasurer, Bradshaw H. Swales, Detroit. Two permanent committees were created. The

committee on Geographical Distribution consists of Dr. Charles C. Adams (chairman), Ann Arbor; Professor Walter B. Barrows, Agricultural College; Bryant Walker and B. H. Swales, of Detroit. The Bird Protection Committee consists of Edward Arnold (chairman), Battle Creek; Professor Walter B. Barrows, Agricultural College; James B. Purdy, Plymouth, to act in conjunction with Wm. Dutcher, chairman of the Protection Committee of the American Ornithologists' Union.

It was decided to continue the former club journal styled the Bulletin of the Michigan Ornithological Club, three numbers of which (Vol. IV.) have appeared so far. Alexander W. Blain, Jr., was made editor and business manager, and later J. Claire Wood, of Detroit, and Adolphe B. Covert, of Ann Arbor, were elected associates. The Bulletin is published by the club at Detroit as an illustrated quarterly devoted to the ornithology of the Great Lake region.

The prospects for the Ornithological Club in the Wolverine state seem most bright, and the society already has over one hundred members enrolled.. Monthly meetings are held on the first Friday of each month at the Detroit Museum of Art and annual meetings will be held at the same time and place as the annual meeting of the Michigan Academy of Science. ALEX. W. BLAIN, JR. DETROIT COLLEGE OF MEDICINE.

DISCUSSION AND CORRESPONDENCE.

MICHIGAN PLANT SOCIETIES AGAIN.

THE thorough remodeling which my paper on the upland plant societies of Kent County, Mich.,* received at the hands of Mr. Francis Daniels in SCIENCE for August 14, 1903, makes this note by the author seem necessary. In the first place, I hasten to acknowledge with thanks the two very bad blunders which the reviewer has pointed out. Quercus ilicifolia should read Q. prinoides, and Vitis cordifolia should be replaced by V. riparia.

In the original paper the author expressly

* Annual Report State Board of Geol. Survey, Mich., 1901, pp. 81-103. Botanical Gazette, 35: 36-55. 1903.

denied all pretense to finality of conclusions; it was to get light on just those subtile changes of soil, etc., to which Mr. Daniels alludes, that the work was undertaken. Thus the criticism that we can not point out any single cause for any difference in vegetation is hardly to the point. My critic deals only with the societies, he is willing to leave the description of soils as it was published.

In

That the societies used are not of equal rank was pointed out by the author. creased complexity would doubtless be accompanied in some measure by increased accuracy, but the main points would thus be almost surely lost sight of in the maze of classification. The systematist born and bred can seldom understand the horribly slipshod ways of the ecologist! The fact that Mr. Daniels puts the beech-maple and the mapleelm-agrimony societies together shows clearly that he has failed to study the southern townships. Farther north these types do tend to merge, but southward, into Indiana and Illinois, they are still distinct, as more recent studies by the author show. Likewise, the combining of the oak-hickory with the oakhazel society indicates failure to study well the condition of things in the northern part of the county. The presence or absence of hickory in this region involves one of the most important ecological questions, one which we can not interpret clearly as yet, but one which it can do no good to slur over. On the whole, my critic's description agrees fairly well with the conditions in the central townships, but fails altogether to express the facts throughout the county as a whole. This is one of the dangers which he might be warned against, namely, that of generalizing from too small an area, no matter how many years he has botanized in it. The author must admit that he, too, is a native of Kent County, and that he has studied its flora for many years.

Bidens frondosa and Solanum nigrum are 'frequent everywhere' only in the moister soils of the Grand River valley. Nepeta, Phytolacca and Euphorbia corrallata are, throughout the area, among the most constant and characteristic members of their societies;

they are not weeds excepting in areas where they originally occurred. Echinospermum occurs in the lowlands, a fact which may have misled Mr. Daniels, but on the uplands it is a truly characteristic plant of the most mesophytic society. Regarding the distribution of Cenchrus there is need of more study than either Mr. Daniels or myself has yet accomplished. Wherever it comes from, it certainly occurs only on the worst sands, i. e., only in the most xerophytic group. Occasional plants of Dracocephalum are to be found in the beech and maple forests south of the Grand River valley.

The societies are based on forms which are evident the year round, not on summer forms nor spring forms. Of the 140 forms listed, no less than 40 are spring-flowering. There doubtless are well-marked societies of Thallophytes and Bryophytes, but those of the two higher groups are the ones chosen for study. An adequate study of the distribution of grasses and sedges will be a work by itself when the right student undertakes it. These plants were purposely omitted from the paper under discussion.

BURTON EDWARD LIVINGSTON. THE NEW YORK BOTANICAL GARDEN, September 15, 1903.

SHORTER ARTICLES.

FOUR NEW SPECIES OF THE CENTRAL AMERICAN RUBBER TREE.

THOUGH still in the initial and experimental stage, the cultivation of rubber-producing trees is now attracting more general attention than any other branch of tropical agriculture. Large amounts of American capital are being invested in Mexico and Central America, and the practicability of rubber culture in the tropical islands of the United States is receiving the attention of the Department of Agriculture. The first studies have been directed to the Central American rubber tree (Castilla), and one of the facts established is the existence of several different local types, instead of a single species extending from Mexico to Bolivia, as hitherto supposed. The species of Castilla are among

the many plants for the study of which the usual dried and shriveled herbarium material is nearly worthless, but in deference to current botanical opinion the public has continued to infer that rubber planting is equally practicable in all localities in which wild trees are found, and that all trees are equally suitable for cultivation, except the elusive 'tunu' or 'ule macho' (male rubber), which Hemsley has recently attempted to separate as a distinct species.

Until the intervening territory has been thoroughly explored it can not be known with certainty whether two supposed species from distinct localities intergrade or not, but for agricultural purposes this is a matter of little importance. There are at least two different kinds of Castilla in cultivation in Mexico and two in Costa Rica, and the indications are that these four are distinct species. The Castilla introduced from Panama to Ceylon and other British colonies represents a fifth type, while three others are of merely botanical interest, as yet, since they are not known to produce commercial rubber.

Before touching upon the characters which distinguish the species, it may be well to explain that Castilla is partially diœcious, somewhat after the manner of the edible fig. The inflorescence consists, as in the fig, of a fleshy receptacle which bears either stamens or pistils; the pistillate inflorescence is turbinate, the staminate more or less flabellate or funnel-shaped. There are trees which bear only male inflorescences, or at least there are some which bear crops of males without females, but along with the females there are also male inflorescences, smaller and generally of a different shape from those of the male trees. The primary male inflorescences arise normally in groups of four, but of the secondary or complemental male inflorescences, those which subtend the females, there are never more than two, as though the female inflorescence were the equivalent of two male clusters.

The original description of Castilla elastica (the name Castilloa being an unwarranted emendation) was not accompanied by any indication of a definite locality, but there is

every probability that Cervantes had reference to the Castilla of eastern Mexico, which seems to differ from all of its relatives in its robust habit and in the large size of its ripe fruits, which also have numerous and very distinct vertical grooves. Cervantes' plate shows, in addition, long, slender complemental male inflorescences.

The Castilla of the Soconusco district of the state of Chiapas (C. lactiflua) is peculiar in having the complemental inflorescence flattened and with a broad mouth; it is very similar to the primary except in the smaller size. The specific name alludes to the fact that the milk of the tree flows freely when the bark is cut, so that it can be collected in quantity and coagulated by improved 'creaming' methods instead of the rubber being harvested wholly or partly by pulling the 'scrap' (burucha) from the gashes in which it has dried. Large yields of scrap rubber are sometimes reported from wild trees, but the tapping to which they are subjected is very severe, and the removal of the rubber from the wounds delays healing and exposes the tree to the attacks of insects, so that the cultural production of scrap rubber is not likely to be profitable.

On the peninsula of Nicoya, which extends into the Pacific Ocean from the northern part of Costa Rica, is a rubber tree easily recognized by the dark olive color of its inflorescences of both sexes, and by the deeply bilobed, long-stalked primary male inflorescence; the complemental inflorescences are also long and slender and are usually grown together at the base. The branches, leaves and floral organs are also much more densely hairy than those of the Castilla or of the more humid eastern slope of Costa Rica (C. costaricana Liebmann). In C. nicoyensis the individual fruits are very prominent, as in the two Mexican species, but in C. costaricana they are separate only at the broadly rounded or flattened apex, leaving no characters by which Hemsley's Castilla tunu, from British Honduras, can be distinguished, except the reputed deficiency of rubber, which is by no means lacking in C. costaricana. It seems certain, however, the 'tunu' tree which Hemsley has recently figured and described from