380 General Notes. 
fore he sat down to prepare his great scientific work on Peru for pub- 
lication. This first volume is the key to the whole work, for it describes 
the methods and instruments used in the various branches of science, and 
contains a most interesting personal narrative of the author’s numerous 
journeys, during nineteen years, over the length and breadth of the land. 
The work itself will consist of six parts. The first will be devoted to 
geography and meteorology, the second to geology, the third to mineral- 
ogy, the fourth and fifth parts to botany and zodlogy, and the sixth and 
last to ethnology, including descriptions of the architectural remains, pot- 
tery, arms, etc., of the different Peruvian tribes. 
RECENT Rine OF THE Peruvian Coast. — Interesting illustrations 
of the comparatively recent change in the coast level of Peru and 
the geographical changes resulting, are afforded by Mr. A. a in 
the last Bulletin of the Museum of Comparative Zoölogy. A number 
of corals were found by him at the height of from 2900 to 3000 feet 
above the level of the sea, at a distance in a straight line from the Pacific 
Ocean of twenty miles. From the general features of the country along 
the coast of Peru, it requires but little imagination to reconstruct the 
former internal sea formed: by the Coast ‘Range; which must have, 
within comparatively recent geological times, covered the whole of the 
great nitrate basin of Peru, and which has gradually been elevated to 
its present position. This inland sea then became a salt lake, after- 
wards a lagoon, and finally was entirely drained. While Darwin showed 
that beyond doubt the coast of South America has been recently ele- 
vated 800 feet, Mr. Agassiz believes that the elevation reached an alti- 
tude of at least 2900 feet, and in earlier times, judging by the marine 
nature of the fauna of Lake Titicaca, to an elevation of 12,500 feet. 
[ June, 
MICROSCOPY.! 
Tae Limits or Microscopic Vision. — In his recent annual ad- 
dress to the Microscopical Society of London, the president, Mr.’ H. C. 
Sorby, F. R. S., discusses the relation between the limits of the powers 
of the microscope and the size of the ultimate molecules of matter. As 
the combined result of observation and theory, he concludes that the 
normal limit of distinct visibility with the most perfect microscope is 
one half of the wave-length of the light. If so, even with the very best 
lenses (except under special conditions) light itself is of too coarse & 
nature to even enable us to define objects less than gyda tO 100000 
an inch apart. It would appear, therefore, that as far as this question is 
concerned, our microscopes have a ready reached their ultimate limit. 
Adopting the results as to the size of the ultimate molecules of matter 
arrived at by Mr. Stanley, Sir W. Thomson, and Professor Clerk-Max- 
well, Mr. Sorby calculates that in the smallest interval which could be 
distinctly seen by the best possible microscope, there would be about 
1 This department is conducted by Dr. R. H. Warp, Troy, N. Y. 
