146 Scientific Intelligence. 
- close of August or beginning of September showed that a hori- 
zontally adjusted dinner plate of about 93 inches diameter was 
visible at noon at a depth of 108 feet. The maximum depth of 
the limit of visibility as found by Professor Forel in Lake Geneva 
was 56 feet ; he showed, moreover, that this limit is much greater 
in winter than in summer as explained in part by the greater 
absence of suspended matter and in part by the fact that increase 
of temperature increases the absorbing power of water for light. 
The maximum depth of visibility in the Atlantic Ocean, as found 
by Count de Pourtales, was 162 feet, and Professor LeConte 
states his belief that winter observations in Lake Tahoe would 
place the limit at even a greater depth than this. The author 
gives a detailed and interesting discussion in regard to the blue 
color of lake waters, reviewing in full the results of previous 
writers on the subject, and concludes that while pure water un- 
fine particles suspended in it. 
The last subject discussed by the author is that of the rhythmical 
variations of level, or “seiches,” of deep lakes; he applies the usual 
formula to Lake Tahoe and calculates from it the length of a com- 
sag longitudinal, and of a transverse “seiche;” these are found to 
e 18 or 19 minutes in the first case and 13 minutes in the second. 
» Il. Grotogy AND MINERALOGY. 
1. Geology of Wisconsin, Survey of 1873-1879; T. C. 
CaamMBERLIN, Chief Geologist; vol. I, xxiv and 726 pp. 8V®, 
with maps and figures; and vol. IV, xxiv and 780 pp., with 27 
plates of figures 2 fossils, in 8vo, maps and sections in the text, — 
1 
vablished in 1877 and volume III in 1880. 
special interest and value, because of the range of the geologl- 
cal formations arid their products, and also the able treatment of 
the various subjects that come under discussion. - = 
Of the new volumes, volume I contains a popular review by 
introduced; and also other brief reviews of the facts connected _ 
with the subject of minerals and rocks, by R. D. Salisbury and 
. Irving; lists of fossils, plants, crustaceans, lepidopters: 
elaborate paper OD th 
by F. H. Ki 
the State, by Moses Strong, and another on the Lower St. Ce 2 
district, by L. C. Wooster; a Paleontological Report, by RF 
