THE FOCAL LENGTH OF MICROSCOPIC OBJECTIVES. Mr. C. R. Cross has ably discussed this subject in the "Franklin Journal." He remarks: "The investigation of which the present article is a summary, was undertaken in order to see if some reliable method of measuring the focal length of microscope objectives could not be found. The importance of such a method will be apparent to all who have had occasion to make use of objectives by different makers. The focal length of lenses of the same denomination is subject to so great a variation that comparison of these by means of their assumed focal lengths too often gives no true idea of their relative excellence. For example, if two quarter-inch objectives be compared, and one gives results much superior to that given by the other, we cannot be at all sure that the better lens is not really of shorter focus than its designation would indicate." He presents a table giving "the results of several hundred measurements on various objectives, and suggests that an examination of the table will show that the focal length of the objectives of some makers differs considerably from the length marked upon them. For example, No. 34 marked 1-2 inch is really a 1-3 inch objective; No. 33 marked 1-4 inch is really a 1-5 inch; No. 29 marked 4-10 inch is really a 1-4. Lens No. 14, marked 1-4 inch, is really a 1-5 inch; but Nos. 13, 15, by the same makers, are correctly designated 1-5 inch, 2-3 inch. Differences of this kind must of necessity lead to a great confusion in comparing objectives with one another. I would therefore suggest that each objective made should be measured before being offered for sale, that this confusion may cease to exist. A convenient arrangement would be to fix a glass scale divided to 1-50 or 1-100 inch in the drawtube, sliding in the tube of the microscope, and measure as I have already described. The draw-tube should be moved till the front of the ruled glass shall be exactly 10 inches from the micrometer used as the object. Or it would be more convenient still to have an apparatus similar to the first form, but arranged with a suitable stage and stand so that it can be set at any desired angle. The distance 10 inches (254mm.), suggested as a standard is chosen because it is the normal distance of distinct vision, as well as about the length used by microscopists in actual work.” ANTHROPOLOGY. PERUVIAN ARCHÆOLOGY. - The extent to which the conditions of mankind are influenced by natural circumstances, and how these may dictate, not alone the architecture and arts of a people, but their social, religious and political organizations, is perhaps nowhere better illustrated than in Peru. The Inca Empire, it seems to me, was only rendered possible by the peculiar geographical and topographical position occupied by the family or families that were its founders. Long antedating that empire its vast area contained a great number of communities, tribes, or principalities, more or less advanced or civilized, separated from each other, however, on the coast, by hot and almost impassable deserts, and in the interior by lofty mountains, or cold and trackless punas. They had but little intercourse or political dependence, and they all, when by means of alliance or conquest the enterprising families around Cuzco became consolidated, fell an easy prey to those inhabitants of the high, strong fastnesses, or bolsones, of the Andes. From their dominating position the Incas were enabled to throw overwhelming forces successively on the isolated valleys radiating from their mountain centre, and one by one mold them into the grandest of aboriginal American Empires. It is easy to see how ambition, and the exigences arising out of their aggressions, should have developed gradually that astute policy or statesmanship, that ability in organization and administration, of which the Incas furnished such a remarkable example. That portion of the Andean plateau lying between the Pass of La Raya, at the northern extremity of the Titicaca basin and the Pass of la Banda, near Pasco, is a great mountain-encircled region, drained by the River Ucayali, itself, as we have seen, formed by the Vilcamayo, Apurimac, and Pampas flowing north, and the Mantaro flowing south. The beds of these streams are deep and narrow, being merely gigantic canals or drains for the waters collected in numberless vales among the mountains. Nothing better describes these vales than the Spanish word bolson, or pocket. And, as I have said, while the valleys of the coast are separated by deserts, these bolsones are isolated by ranges of hills, mountains, or uninhabitable punas, and all these are divided into groups by the great rivers, which, like the Apurimac, are intransitable except by the aid of bridges of mimbres, or ropes swinging dizzily in mid-air. These bolsones are of varying altitudes and consequently of various climates and productions. Some are well-drained, others are marshy, and contain considerable lakes. They discharge their gathered waters, often in large streams that plunge, in numberless cataracts, through dark and narrow ravines into the gorges of the great rivers. The passage from one bolson to another is over the intervening elevated ridges and punas, frequently among frost and snow, and always by rocky and difficult paths, fit only for the goat and the llama. It was in precisely one of these bolsones, the central one of a group or cluster lying between the Vilcamayo River and the Apurimac, that the Incas built their capital. It is not only central in position, salubrious and productive, but the mountain barriers that separate it from its neighbors are relatively low, and subside into passes that may be traversed with comparative ease, while they are at the same time readily defensible. The rule of the first Inca does not seem to have extended beyond this valley, and the passes leading into it are strongly fortified, with works that face outward, indicating the directions whence attack was possible in the early days of the empire, before the chiefs of Cuzco commenced their career of conquest by reducing the people of the bolson of Anta or Xaxiguana on the north, and of Urcos or Andahuaylillas on the south. The bolson of Cuzco, which is not far from thirty miles long, is divided into two nearly equal parts by the Pass of Angostura, or the narrows, where the mountain spurs project toward each other into the valley, leaving hardly room enough for the roadway and the river. On the promontories dominating this narrow passage are the conspicuous ruins of many buildings and remains of works, showing that this was regarded as a strategic or important position, for the immediate protection of the capitol. The City of Cuzco, which occupies the site of the ancient capitol, stands at the northern or most elevated extremity of the bolson, or valley, on the lower slopes of three high hills, the Carmenca, Sacsahuaman, and Cantuta, where as many rivulets, the Almodena, Huatenay and Tullamayo, or Rodadero, coming together like the fingers of an outspread hand, unite to form the Cachamayo, which drains the valley, and falls into the Urubamba. The old city, or rather that part of it dedicated to the royal family, was built on the tongue of land falling off from the hill or headland of the Sacsahuaman, between the Huatenay and the Rodadero. The position of this city, as determined by Mr. Pentland, is latitude 13° 31' S., and longitude 72° 2′ W. of Greenwich. Its elevation above the sea, eleven thousand three hundred and eighty feet. Surrounded by high and snowy mountains, it might be supposed to have a cold, not to say frigid climate, but in fact its temperature, though cold, is seldom freezing, and although in the dry season, or what is called winter, from May to November, the pastures and fields are sere, and the leaves fall from all but queñua trees, yet all this is rather from drouth than frost. On the whole the climate is equable and salubrious. Wheat, barley, maize, and potatoes ripen in the valley, and the strawberry, apricot, and peach are not unknown. The climate of Nismes, and of the south of France generally, is much the same with that of Cuzco. When we add to these favorable conditions that not more than thirty miles distant are deep, hot valleys, where semi-tropical fruits may be produced abundantly, we may comprehend that Cuzco was not an unfavorable site for a great capitol. Its geographical position as regards the country at large, as I have said, was also such as to make it a citadel and the dominating centre of an empire. Its very name, if we may credit the chronicler, signified Umbilicus. The Inca power once fairly established in the cluster of valleys, of which I have spoken, and the few and narrow passes by which only they can be reached, strongly fortified, as they were, it was comparatively easy, as I have already said, for the Incas to overwhelm the inhabitants of the long and narrow valleys running down the slopes of the Andes and the Cordilleras, and to subdue one by one the families dwellIng in the bolsones northward to the Equator, and southward below the desert of Atucama-over an extent of thirty-seven degrees of latitude. -E. G. SQUIER, from Lecture on Peruvian Archæology delivered before the American Geographical and Statistical Society, February 15. ANSWERS TO CORRESPONDENTS. - E. S. Miller. Your specimens reached us in such a decayed condition that it was difficult to recognize them, and after careful study we made out the species as follows: No. 1, Pontederia cordata; No. 5, Ranunculus, perhaps R. parviflorus, but the sperimen was insufficient; No. 6, Lobelia spicata; No.-, a coarse plant, and is Lithospermu No., Hypericum mutilum: No.-, Gratiola aurea; No. —, Schollera graminea. Speci mens of plants should be carefully pressed and dried, and never sent fresh, unless intended for cultivation. The deficient numbers were of tickets either destroyed by the heat or fermentation, or torn accidentally on opening the package. We do not want any of the kinds sent as they are common hereabouts, though we thank you for your offer.-J. L. R. Proceedings of the Acad, of Nat. Sciences. Phil. January, February, March and April, 190, Trout Culture. By Seth Green, Rochester, 1870. The Academy. No. 9. June, 1870. Annual Report of the Trustees of the Museum of Comparative Zoology for 1869. Thirty-three Ornithological pamphlets. By Geo. N. Lawrence. Fifty-second Annual Report of the Trustees of the N. Y. State Library. Albany, 1870. Cranberry Culture. By Jos. J. White. Glimpses of Nature. S. M. Maxwell. Chemist and Druggist. London, July 1, 15, 1870. Verhandlungen der K. K. zoologisch botanischen Gesellschaft in Wien. Band, xviii, 1868, xix, 1869. 2 vols. 8vo. Zeitschrift fur Akklimatisation. 1868. Nos. 1-12. 1869. Nos. 1-12. 8vo. Berlin. Sitzungs-Berichte der Gesellschaft Naturforschender Freunde. Berlin. 4to. 1865-69. Abhandlungen herausgegeben von naturwissenschaftlichen Vereins zu Bremen. Bd. 2, Heft. 2. 8vo. 1870. Die Vegetationsverhaltnisse Von Croatien. 8vo. Wien, 1868. Von Dr. August Neilreich. The Transactions of the Entomological Society of London, 1869. The lifted and subsided Rocks of America, with their influences on the Oceanic, Atmospheric and Land Currents and the Distribution of Races. By Geo. Catlin. London, Trubner & Co. 1870. 12mo. Grammar of the Choctaw Language. From the MSS., by D. G. Brinton. M. D. National Legend of the Chata-Muskokee tribes. By D. G. Brinton. M. D. Contributions to the grammar of the Muskokee Language. By D. G. Brinton, M. D. The Ancient Phonetic Alphabet of Yucatan. By D. G. Brinton, M. D. American Scientific Monthly, Vol. 1. No. 1. July, 1870. G. Hinrich, Iowa City, Iowa. Proceedings of the California Academy of Science. Vol. 1. Part 2. 1870. Quarterly Journal of Science, London, July, 1870. American Journal of Conchology, Vol. 6. Part 1, 1870. Field. July 2d and 9th. London, 1870. Cosmos. July 2d, 9th and 16th. Liv. 1, 2, 3. Address on the Natural History and Pathological Osteology of the Horse. By N. Cressy, M. D. Middletown. Jan., 1870. Bulletin de la Societe Imperiale des Naturalistes de Moscow. Nos. 1, 2, 3. 8vo. Moscow, 1889. Annales de la Societe Entomologique de France. 8vo. 1869. Paris, Verhandlungen des naturhistorischen Vereins du preussichen Rheinland und Westphalen, 8vo. 26th Jahrgang, Halft. 1, 2. Bonn. 1869. Peat Fuel; how to make it, and how to use it. What it costs and what it is worth. T. H. Leavitt. Boston: Lee & Shepard. 12mo, pp. 62. 50 cts. Le Naturaliste Canadien. Vol. 2. No. 8. July, 1870. Land and Water. 4, 11, 18 and 25. July. English Mechanic and Mirror of Science. July 8, 15, 1870. Vol. xi. Nos. 276, 277. Tiddskrift for Populære Fremstillinger af Naturvidenskaben. Copenhagen. June, 1870. Bulletin Mensuel de la Societe Imperial Zoologique d' Acclimatation. Tome 7. June, 1870. Nature, June 30 to July 7, 1870. The Man who Advertises and American Newspaper Rate Book. Royal 8vo. Rowell & Co. New York, 1870. Speech of Hon. Geo. F. Hoar on Universal Education. Revue des Cours Scientifiqes de la France et de l'stranger. Paris. Dec. '69 to June 70. 4,8, 11 of and 2,9 and 23, July, 1870. Petites Nouvelles Entomologiques, Nov. 25 and 26. The North American Lakes, considered as Chronometers of Post Glacial Time. By Dr. Edmund Andrews. Royal 8vo, pp. 23. THE AMERICAN NATURALIST. Vol. IV. - OCTOBER, 1870.- No. 8. RECENT ADVANCES IN GEOLOGY.* BY J. W. FOSTER, LL. D. Mr. President, and Gentlemen of the American Association for the Advancement of Science: THERE is an article contained in our Constitution which requires the retiring President to address the Association in general meeting; and custom has prescribed that he select for his theme some new and important discoveries in science, or some new inventions and processes in the arts. It is in the discharge of this duty that I appear before you on this occasion, and solicit your attention for the passing hour. So vast is the domain of science, and so numerous have become its cultivators in almost every part of the world, that, even if I had the capacity, the labor of embodying the results of a single year, in a brief address, would be a mere accumulation of details devoid of that spirit which gives them value--generalization. I shall, therefore, restrict myself to the researches which have been made in those departments of science which with me have been the subjects of special investigation; and shall Address of the retiring president of the American Association for the Advancement of Science, J. W. Foster, LL. D., delivered at Troy, New York, on the evening of August 18, 1870. Entered according to Act of Congress, in the year 1870, by the PEABODY ACADEMY OF SCIENOR, in the Clerk's Office of the District Court of the District of Massachusetts. AMER. NATURALIST, VOL. IV. 57 (449) |