1 882.] Scientific News. 433 



even such elegant works as Wood's Fresh-Water Algae, Leidy's 

 Fresh-Water Rhizopods, Zirkel's Microscopical Petrography, and 

 Sullivant's Icones Muscorum. On the other hand, the American 

 style of naming oculars by their degree of amplification, as 

 2-inch, 1 -inch, etc., is noted with approval; as is also the adop- 

 tion of the metric system in micrometry, and especially the 

 selection of the one-thousandth of a millimeter, under the name 

 of micro-millimeter or micra, as the unit to be employed. 

 The question of angular aperture, and of testing objectives, 

 is discussed with candor and freshness. The later chapters of 

 the book treat of collecting objects, dissections, section-cutting, 

 drawing and measurements, polariscope, micro-spectroscope, 

 staining and injecting, and preparing and mounting objects. 

 While giving recipes for various reagents and mounting media 

 and cements, the author offers the very sensible advice that 

 parties who require only small quantities should purchase them 

 from a dealer instead of attempting their manufacture. He 

 also advises against the use of "secret nostrums." Natural his- 

 tory subjects, which form so large a part of some of the manuals, 

 are only touched upon incidentally. The work is freely illus- 

 trated, though only_one of the plates is accompanied by a scale 

 showing the magnifying power employed. 



SCIENTIFIC NEWS. 

 — In the Kansas City Review, Mr. L. F. Ward gives the 

 following sensible views as to the reasons why the Western 

 plains are destitute of forests. He considers that the prairies 

 are without forests, because of fire set by Indians : Since the 

 elevation of the Rocky Mountain range at the close of the 

 Tertiary age, the atmosphere, in the general easterly move- 

 ment which it possesses at all latitudes within the United 

 States, has at all times lost the greater part of its moisture by 

 condensation upon the cold summits of these and the more wes- 

 tern ranges, so that by the time it reaches the great plains it is 



' precipitation except under 

 I furtl 



moves still further eastward across a level country, having river 

 valleys and lake basins, it comes in contact with currents from the 

 north, the south and the cast, brought there by the constant dis- 

 turbances of barometric pressure with which all are acquainted, 

 and in this manner it gradually becomes at length again suffi- 

 ciently laden with moisture to yield portions ot it to the soil when 

 condensed by currents of unlike temperature. This characteristic 

 becomes more and more marked with the eastern movement until 

 the Missis. i n which and at all pomts east- 



ward the rain-fall, varving from thirtv-twoto sixty inches is suffi- 

 cient to be depended u purposes. 



Where the annual precipitation is below twenty, or perhaps 



