486 



SCIENCE. 



[N. S. Vol. V. No. 11«. 



ingly neat instrument for determining the fre- 

 quency of an alternating current. A small 

 synchronous motor is connected through a train 

 of gears to a dial which indicates the frequency 

 direct. The apparatus is small and portable, 

 the base being 14 inches long and the total 

 weight being 8.5 pounds. It may be operated 

 from a 16 candle-power lamp socket. 



Lecture- Room Demonstration of Orbits of 

 Bodies Under the Action of a Central Attraction: 

 By R. W. Wood. The apparatus consists of 

 an electro-magnet with a conical pole piece pro- 

 jecting through a horizontal glass plate covered 

 with lampblack. A bicycle ball is shot out 

 upon this plate ; its path is traced and a per- 

 manent record of its motion is thus obtained. 

 Various orbits were thus determined. 



Tlie Refractory Index of Water and Alcohol for 

 Alcohol and Electrical Waves : By A. D. Cole. 

 This short note calls attention to the fact that 

 the writer in a previous paper had not ignored 

 the absorption of the Medium. 



New Books : Higher Mathematics, Merriman 

 and Woodward ; A Primer of Quaternions, Hath- 

 away ; Alternating- Current Machinery, D. C. and 

 T. C. Jackson ; Transformers for Single and 

 Multiphase Circuits, Kapp ; Methods et principes 

 des sciences naturelles, Brentano ; Elements of 

 Electro- Chemistry, Le Blanc ; Motive Power and 

 Gearing for Electrical Machinery, Carter ; Mathe- 

 matical Papers read at the International Mathe- 

 matical Congress, Chicago, 1893; Laboratory 

 Manual of Inorganic Chemistry, Williams ; Chem- 

 istry at a Glance, Tuttle ; Inorganic Chemical 

 Preparations ; The American Annual of Photogra- 

 phy, Thorp ; Problems and Questions in Physics, 

 Matthews and Shearer. 



AMERICAN GEOLOGIST, MARCH. 



O. W. Crosby and M. L. Fuller present 

 the results of their investigation as to the 

 ' Origin of Pegmatite,' or giant granite. The 

 intimate association and evident close connec- 

 tion of pegmatite with undoubted plutonic 

 rocks, and their agreement with the latter in 

 composition and relations to the inclosing for- 

 mations, have led many writers to regard the 

 pegmatite itself as of plutonic igneous origin. 

 It is also not long since geologists were united 

 in the conviction that these were true vein rocks. 



due to the deposition of the various component 

 minerals from solution in open fissures or other 

 preexisting cavities. Now, however, a decided 

 drift in the opposite direction may again be 

 noted, and recent literature indicates an ap- 

 proaching agreement in favor of the association 

 of the pegmatites, in their genetic relations, 

 with plutonic igneous rocks rather than with 

 subterranean aqueous deposits. The authors 

 conclude that the magma of pegmatite may be 

 formed by normal magmatic differentiation in a 

 boss, or large body of magma, both crystalliza- 

 tion and the operation of different temperatures 

 in various parts of the mass tending to increase 

 the degree of hydration of the residuum about 

 favorable centers. These magma residues may 

 crystallize in situ, in the midst of the previ- 

 ously solidified normal granite, or they may 

 suffer extravasation and crystallize in spaces in 

 the parent rock or in the surrounding forma- 

 tions. Also, apophyses of the normal granite 

 magma may invade highly heated, water-bear- 

 ing formations, such as schists, and experience 

 the necessary hydration for conversion into peg- 

 matite magma. 



The correlation papers on ' The Galena and 

 Maquoketa Series,' by F. W. Sardeson, end 

 with this number. The basis employed has not 

 been the usual one of computation of percent- 

 ages among the various beds, but the limits, 

 range, distribution and variation of the com- 

 monest species has been taken. 



' Evidence of Glaciation in Labrador and 

 Baffin Land,' by R. S. Tarr. All of the land, 

 excepting possibly the highest parts, has been 

 buried beneath an ice sheet. The glacial ac- 

 tion produced more effect in the down-cutting 

 of the surface in Labrador than in Baffin Laud, 

 and there is evidence that the ice has with- 

 drawn from these regions in very recent times. 

 Ice erosion has been greater in New England 

 than in the northern region. On the other 

 hand, proceeding northward, the effects of post- 

 glacial weathering become progressively pro- 

 nounced, so that the recency of the ice uncov- 

 ering is more and more marked. 



O. H. Hershey has the first installment of a 

 paper on 'Esker's indicating stages of glacial 

 recession in the Kansan epoch in Northern 

 Illinois.' 



