There were others who supposed it to be going towards the zenith. Two reliable observations further afforded him the means of calculating with some certainty, both the direction and the height. One of these was the observation made in the Münster Cathedral. The large west window of the cathedral was suddenly lighted up, so that the architectural details were all rendered plainly visible, and the observer saw the ball pass across in an oblique direction from the right-hand corner. From measurement of the distance of the observer from the window, and the height of the window, Dr. Heis was enabled to calculate two points in the path of the Meteor.

We may sum up, in a few words, the conclusions at which the author arrived from a careful comparison of the various observations which reached him. He believes that the fire-ball first became visible at a point in the North Sea, about 53° 50′ north latitude, and longitude 5° east of Greenwich, at a height of 88 miles; that it travelled from north to south, and disappeared in latitude 51° 28', longitude 5° 18', at a height of 17 miles, having in its visible course traversed 187 miles in 4 seconds, at the rate of 47 miles in a second. The path inclined towards the horizon, at an angle of 22°.

We have said that the author himself believed that the fire-ball had fallen to the earth. So convinced was he of this, that he made a journey to the place near which he supposed it to have fallen, in order to search for and make inquiries after it. He wandered over the neighbourhood of Herzogenbusch, in the north of Flanders, for several days, but without success, and departed at last, disappointed indeed, yet still hopeful, for he left at the village schools a promise of a large reward for any boy who should find a meteoric-stone.

On all sides, however, he found the impression existed that the Meteor had fallen in the immediate neigbourhood, and from the interval of time which elapsed between the disappearance of the light and the observation of the sound in this vicinity, he calculated the height at which it exploded. But unfortunately the ideas of the Belgian peasants as to length of the interval were rather vague. Several guessed it at five minutes, which was much too long, so the Doctor, in his perplexity, appealed to an intelligent cook, who both saw the Meteor and was frightened by the noise. In answer to the question, "Could she have boiled an egg hard in the interval?" she replied, "Lord bless me, no-not even soft!-Lord bless me, no; it could not have done in double the time;" and so the interval was reduced from five minutes to less than one minute, which was further diminished by other observers to twenty-two or twenty-five seconds.

If it were solid, and had fallen entire, there would hardly have been much difficulty in finding the object, for Dr. Heis has calculated that in such a case the earth would suddenly have acquired a mountain as large as one of the Siebengebirge. The diameter of the fire-ball he estimates at 1,381 English feet; but it may be, he remarks, that these bodies have only a small nucleus within a luminous envelope.

The cosmical relations of the fire-ball of the 4th of March we must dismiss very briefly. The author determined that it moved around the

sun in a hyperbola, and that it became visible at a point in the heavens near the star y Cephei. For the elements of this determination we must refer the reader to the little work under review.

With regard to the chemical composition of fire-balls, Dr. Heis has nothing new to tell us. The recent discovery of hydrocarbons, graphite, and free sulphur in stones which have fallen, may lead to the supposition that some are wholly combustible in very attenuated air, and we may thus account for the phenomena of falling or shooting-stars; while in others the mineral matters may predominate, and these sometimes exploding with detonation, fragments fall to the earth constituting meteoric stones.

Respecting the origin and destination of the Meteors and fire-balls we have, of course, no information, and the votaries of modern science and of ancient poetry will still continue variously to regard them as fresh fuel for our flaming sun, or fragments of a shattered world.

MILLS AND MILLWORK.*

To the minds of laymen the vocation of engineering is not so obviously cut up into distinct departments as the better known and older professions. While time and the experience which each of us must encounter teach all men to distinguish, with some approach to accuracy, between the many distinct provinces into which the practice of medicine and that of law are divided, there are comparatively few persons not connected with engineering who are aware that the same division of labour which characterizes each of the three so-called learned professions may be found to regulate and aid the labours of the engineer. The two main lines of the calling are pretty well known under their relative names of Civil, and Mechanical Engineering; but out of these, and especially out of the latter, there spring numerous entirely distinct branch lines, each leading and ministering to its own special industry, and each (to carry out our figure) presided over by a distinct staff of management with widely different functions.

The civil engineers being a more purely professional class than their mechanical brethren, naturally deal with a wide range of matters, and do not greatly tend to split up into specialities; but the mechanician being generally a practical man who lives by producing as well as scheming machinery, soon finds that his business, to be made profitable, must be confined within comparatively narrow limits.

Hence there arises an immense variety of machine makers, all included under the generic title of mechanical engineers, a body amongst whom, taken as a whole, there exists an astonishing amount of practical experience and theoretical knowledge; but each having his own speciality out of which it is seldom his wish or his interest to travel.

This is, however, quite a recent state of things in the profession.

Mills and Millwork.' By W. Fairbairn, Esq., C.E., LL.D., F.R.S., F.G.S., &c. 2 vols. Longmans.

Some fifty years ago, when the machinist's art was in its infancy, the "millwright," who may fairly be considered as the ancestor of mechanical engineers, was far from special in his pursuits. In the best cases he was, to use Mr. Fairbairn's own words, "the sole representative of mechanical art. He was the engineer of the district in which he lived; a kind of Jack-of-all-trades who could with equal facility work at the lathe, the anvil, or the carpenter's bench. Generally he was a fair arithmetician, knew something of geometry, levelling, and mensuration, and, in some cases, possessed a very competent knowledge of practical mathematics. He could calculate the velocities, strength, and power of machines; could draw in plan and section, and could construct buildings, conduits, or water-courses in all the forms and under all the conditions required in his professional practice; he could build bridges, cut canals, and perform a variety of work now done by civil engineers. Such was the character and condition of the men who designed and carried out most of the mechanical work of this country up to the middle and end of the last century."

In the course of the great modern expansion of the mechanical arts, the old millwright has become very nearly extinct, and the wide field in which he laboured has been partitioned among several craftsmen. The domain of mill-work is, however, still very comprehensive, while it is not surpassed in importance by any other branch of mechanical industry.

Mill-work may properly be said to include every engineering process involved in the construction both of the buildings and machinery employed in producing consumable manufactures, including every species of motive power, whether derived from wind, water, or steam. Mr. Fairbairn's book is a practical and, in some particulars, an exhaustive treatise on each of these subjects, which are judiciously divided into five sections, comprising 1. Introduction, with a sketch of the early history of mills. 2. The principles of mechanism. 3. On prime movers. 4. On the machinery of transmission. 5. On the arrangement of mills. Of the two first sections we have little to say; both might have been omitted without detriment to the merits of the work; it is only after we have skimmed the curious information of the first, and glanced at the familiar elementary mechanics of the second section, that we begin to find the great storehouse of the author's original experiences open, or to recognize what an enormous amount and variety of actual practice is here reduced, tabulated, and made ready for the daily use of the millwright and engineer.

Throughout the whole of his work, but especially in the second and latest published volume with which we have more particularly to deal, Mr. Fairbairn is essentially "practical." It is a noteworthy fact that in spite of the aid which mathematical science affords to the engineer, our best machinists and our best machinery are less the result of applied mathematical investigation than of intuitive judgment backed by the time-honoured rule of thumb. It is true that the mathematician's aid is in every-day use in ascertaining the direction and intensity of strains and calculating the resisting powers of the various parts of machinery, but even through all the elaborate tables and rules given

by our author for the determination of the proportions of gearing, shafts, or any other portion of mill work, the fact transpires, that the mathematics have been fitted to the practice, and not the practice to the mathematics. Nor is this peculiar to Mr. Fairbairn; on the contrary, a similar tendency has pervaded the work of our best engineers, so that it has almost come to be believed by some, that a great mathematical capacity is inconsistent with unusual mechanical ability.

Though this is a question of much interest, we do not propose to discuss it here, but merely remark, in passing, that Mr. Fairbairn's work is certainly another and weighty argument put into the mouths of those who hold that the great masters in the mechanical craft have ever used pure mathematics as a very humble kind of servant, treating her mainly as a custos rerum, or a means of making the results of their great natural intuition and observation common property for their inferiors or successors.

The second and recently published volume of the work opens with Section 4, and contains an elaborate investigation into the wide subject of the machinery of transmission. Amongst one of the most important general conclusions on this subject, towards which Mr. Fairbairn conducts the reader, is that of the superiority of toothed gearing over straps or other wrapping connectors for purposes of transmission. It is well to have our attention called to this point at a time when the example of American engineers has produced a strong feeling in favour of strapping as compared with gear, and Mr. Fairbairn does good service in pointing out the superiority of wheelwork. The advantages which can be claimed for straps are smoothness of motion, noiselessness of action, and perhaps smallness of first cost; but they are cumbrous, frequently out of repair, destructive in their effects on the journals, and wholly inapplicable in cases where the motion requires to be transmitted in a constant ratio. One of the drawbacks to a freer use of toothed wheels has hitherto been found in the great expense of truly shaped and fitted gears; but the introduction of the wheel-moulding machine, with its consequent improvement in the truth of teeth in cast-wheels, is likely to bring wheelwork into more extensive use than at present.

The chapters on the teeth of wheels would be little more than a recapitulation of the ordinary mathematical demonstration of their true form were it not for the introduction of a most useful series of practical tables, from one or other of which, as if from a ready reckoner, every problem concerning any required wheel may be instantly solved, whether it relate to the strength, pitch, thickness, depth, clearance, or horses' power to be transmitted through a particular tooth.*

*Among the drawings given of various forms of teeth is one which, like the table just referred to, illustrates the very practical nature of this treatise. Our mechanical readers are, of course, aware that in most demonstrations of the Epicycloidal tooth that particular form having its flanks formed by hypocycloids, which are also radial lines, is almost exclusively dealt with. Now this is a tooth which, notwithstanding the simplicity of its delineation, is rarely used in practice, because of its inherent weakness; so, although we get, as usual, some prominence given in the demonstration to the radial hypocycloid, Mr. Fairbairn's practical bent does not permit him to leave his reader without giving a figure of the "teeth of a large wheel, traced from one of my own patterns, to exhibit the form which practice has

The remaining chapters on the machinery of transmission deal chiefly with shafting and its details. Next to the practice of dividing labour into minute departments, and making each man's work a task of repetition, the factory system depends for its economy of production on the concentration of a large number of machines under one building. Some years ago, before this plan was carried to its present extent, it was common in mills to have separate water-wheels to every machine; but, as trade developed, the true principle of concentrating the motive power soon forced itself into notice. No sooner did it become the custom to use either one large water-wheel or steam-engine to drive the whole factory, than the question of shafting for the transmission of power to the distant parts of the building began naturally to receive attention. In order to show to what an extent this system of transmission has been carried, we may mention that, at the great Saltaire Mills, more than two miles of shafting is employed. Nowhere, perhaps, throughout his work, does Mr. Fairbairn give more full, accurate, and useful information in a tabulated form than on the subject of shafting, while the practical examples of couplings, clutches, journals, and brackets, illustrated by detail drawings, comprise every modern design of value.

Section 5, on the arrangement of mills, opens with some very interesting remarks and information on mill architecture. It is true that Mr. Fairbairn does not touch at all upon that frequently agitated question, the shortcomings of the engineer as an architect, but his sketches and observations tend to bring it closely before us. A recent writer very well remarked, in speaking of the relations between the engineer and the architect, that, in consequence of the entirely opposite views which either of the two take of their respective professions, the "architects are quarrelling over Greek mouldings and Gothic pinnacles, and dreaming of reproducing the elegance of classical times, while the engineers are spanning our rivers with structures such as the world never saw before, arching under our mountains, and roofing acres for stations. They are, in fact executing a series of works which throw everything else hitherto done into the shade; but all this, unfortunately, without that touch of higher art which is alone wanted for perfection, and this simply because the building profession is divided against itself, because its two branches are conducted on principles so much at variance that they cannot work together. The engineers cannot forego theirs, because they are the only principles which men of sense can follow; so unless the architects will consent to waive some of their archæological fancies, we may be condemned to live in the midst of ugliness for ever. When once this fact is appreciated, we shall surpass all preceding ages in architec

shown to be desirable." In this specimen, as might have been expected, the flanks of the teeth are generated by a small describing circle, whose hypocycloid gives a tooth admirably proportioned and amply strong in the root. This is a small matter, perhaps, but not an unimportant one. No young student of mechanical engineering is likely to be led astray by Mr. Fairbairn, and the teeth of the wheel, "traced from my own pattern," are a good sample of the principle on which the whole of the book is written.