8CIENCE. 



[N. S. Vol. XI. No. 286. 



assumed to be good conductors of electricity, 

 while the interspaces between them are taken 

 to be insulating. According to this assumption 

 the dielectric polarisation must depend on the 

 size and distance apart of the molecules, and 

 therefore on the same elements v/hich regulate 

 the molecular free path ' ' (p. 327). 



§ 123, on molecular forces, makes near the end 

 a more detailed reference to the work of E. 

 Wiedemann on luminous vapors. " He com- 

 pared the light radiated by sodium vapor with 

 that coming from a platinum wire made to glow 

 by the passage of an electric current ; from the re- 

 sistance of the wire and the strength of the cur- 

 rent he could determine the luminous energy in 

 heat units, and compare it with the total heat- 

 energy contained in the vapor. He found that 

 the energy needed for the illumination is vanish- 

 ingly small in comparison with the total energy. 

 An atom, therefore, must be a structure in 

 which pendulous movements can be produced 

 by very small forces." 



§ 124 is an enthusiastic statement of the gen- 

 eral features and possibilities of the vortex atom 

 theory. It is probable that Meyer has never 

 seen the letter written by Lord Kelvin to the 

 late Professor Holman, which ends thus: " We 

 may expect that the time will come v/heu we 

 shall understand the nature of an atom. With 

 great regret I abandon the idea that a mere 

 configuration of motion suflices. " 



This brings us to the mathematical appendices, 

 which extend through 112 pages. The new 

 matter in these is, for the most part, closely 

 connected with the changes already noted in 

 the earlier portions of the book. In several 

 cases the changes in numerical values of im- 

 portant constants are based on the computations 

 of Conrau. 



The translation is well done, though an occa- 

 sional awkward jjhrase may show that the 

 translator's ear for English is slightly and tem- 

 porarily dulled by attention to the original. 

 Thus, on p. 264, ' much too little for there to 

 be found in it,' on p. 270 'has concluded the 

 law,' and on p. 250 'relation' * * * 'which' 

 * * * ' did not succeed in disclosing itself with 

 full clearness.' 



Edwin H. Hall. 



Cambeidge, Mass. 



The Digestibility of American Feeding Stuffs. By 

 Whitman H. Jordan and Frank H. Hall. 

 U. S. Department of Agricultural, Office of 

 Experiment Station, Bulletin No. 77. Pp. 

 100. 



Since farm animals, like man, live not upon 

 what they eat but upon what they digest and 

 assimilate, data on the digestibility of the va- 

 rious feeding stufls are essential for judging of 

 their relative feeding value and for calculating 

 rations for animals under different conditions. 

 Experiments on this subject have formed quite 

 a feature of the work of a number of the agri- 

 cultural experiment stations of this country, 

 and these experiments have accumulated until 

 at present they furnish a comprehensive series 

 of digestion coefficients. The Bulletin brings 

 together the results of these digestion experi- 

 ments up to the end of 1898, and summarizes 

 them in convenient form for use. Of the 378 

 experiments compiled, many of which were 

 made with a number of animals, 59 were with 

 green fodders (grasses and corn), 34 with silage 

 (largely of corn), 143 with dried fodders (hay, 

 corn fodder, etc.), 8 with roots and tubers, 24 

 with grains and seeds, 62 with by-products 

 (brans, gluten feeds or meal, oil meals, etc.), 1 

 with milk, and 47 with mixed rations. The 

 digestion coefiicients are first arranged accord- 

 ing to the stations at which the experiments 

 were made. They are then grouped by classes 

 of feeding stuffs and by the kind of animal 

 (cow, steer, sheep, pig or horse) used in making 

 the experiment. The latter classification gives 

 both the individual experiments and the aver- 

 ages for the different classes of material. It is 

 therefore the one which will be most generally 

 used in practice. In the light of the data pre- 

 sented, the effects of various factors on digesti- 

 bility are considered at some length. Under 

 this heading are included the influence of the 

 kind and condition of the animal used, the 

 stage of growth of the crops, the effect of 

 drying and curing, ensiling, grinding, cooking 

 and moistening of the feed, etc. In many 

 cases the need of more extended data is evi- 

 dent before deductions can be safely drawn. 



The general methods of conducting digestion 

 experiments are described and discussed, to- 

 gether with the limitations of the present 



