July 13, ia*J.] 



SCIENCE. 



45 



to be the number of units of sun-beat Ineiilent per- 

 pentliculaily on a unit-surface, in a unit of time, at 

 the upper limit of the earth's atmosphere; or it is the 

 number of degrees Centigrade a unit-mass of water 

 would be raised in temperature by the sun-lieat inci- 

 dent perpendicularly on a unit-surface, in a unit of 

 time, at the upper limit of the atmosphere. The three 

 units here indicated are, of course, arbitrary. But most 

 physicists, following the example of PouiUet {Comp- 

 tes rendus, vii. 24), take the gram, square centime- 

 tre, and minute, as respectively the units of mass, 

 surface, and time. With regard to time, there is no 

 diversity, the minute beiug universally used; but, 

 for mass and surface, some employ the larger units of 

 a kilogram aiul a square metre, and hence the ap- 

 parent confusion. To obtain a general expression 

 for the value of the 'solar constant,' let 



Q = Quantity of sun-heat incident normally on a 

 unit-surface in a unit of time = solar con- 

 stant. 



S = Area of surface receiving the_heat. 



T = Time of receiving the heat. 



HI = Unit mass of water. 



n = Xumber of u!>it masses of water heated. 



t° = Rise in temperature of the mass of water. 

 Then we have 



Q X S X T — n X. m X t°. 



Consequently, when S, 7", and n are severally equal 

 to unity, we have Q = m x t°; and, when Hi = 1, 

 Q = t° = rise in temperature of a unit-mass of 

 water = value of solar constant in units of heat. 



Now. when the unit of time remains the same, but 

 the units of mass and surface are changed, the value 

 of t° (which measures the solar constant) will be 

 altered, unless both of these units are changed in the 

 same ratio. For, from the equation Q = m x t°, it 



follows that t° varies as . - ; but evidently Q is pro- 

 portional to the magnitude of the unit of surface: 



, „ . unit of surface 



hence t° vanes as — r;^ — t ■? : — • 



unit of mass of water 



For example: using Pouillet's units, Langley's 

 recent experiments malce the solar constant = 2.84; 

 that is, the sun-lieat incident normally on one square 

 centimetre, in one minute, at the upper limit of the 

 atmosphere, would raise tlie temperature of one Hram 

 of water 2.84° C, or would beat 2.84 grams of water 

 1° C. Now, the unit remaining the same, if we 

 assume the unit of mass to be one kilogram (1,000 

 grams), and the unit of surface to be one S(iuare 

 metre (10,000 square centimetres), we should have 



the value of the constant f'° = Ym) ^ "•^'^ ~ -^"^ 

 kilogram-units of heat; that is, the sun-heat incident 

 normally on one square metre, in one minute, at 

 the upper limit of the atmosphere, would raise the 

 temperature of one kilogram of water 28.4° C, or 

 would heat 28.4 kilograms of water 1° C. 



Moreover, as it requires a definite number of units 

 of heat to liquefy a unit-mass of ice, or to evaporate a 

 unit-mass of water, or to produce a unit of mechanical 

 energy, it follows that this constant may be measured 

 by either of these units. 



The exact determination of the v.ilue of this con- 

 stant is a most refined and difficult exi)erimental 

 problem; for it involves the precise estimation of 

 the amount of solar heat absorbed in traver-ing the 

 earth's atmosphere, or the law of extinction of sun- 

 beat in passing through it: hence it is, that, although 

 several excellent physical experimenters have at- 

 tacked the problem, their results are not so accordant 



as would be desirable. 

 the results: — 



The following are some of 



Berkeley, Cal., .Tune 25, 1953. 



John LeCoxte. 



WARD'S DYNAMIC SOCIOLOGY. 



Dynamic sociologij, or applied social science, as based 

 upon statical sociolorjij and the less complex sciences. 

 By Lf.steu F. Ward, A.M. 2 vols. Xew 

 York, ^/)/)/e(on, 1883. 20 + 706; 7 + 690p. 8°. 



I. 



This ivork of Mr. Wartl is composed of two 

 distinct parts.^ The first gives ttie outlines of 

 his philosophy, as a basis for his reasoning in 

 the one that follows. The second is a discus- 

 sion of the causes and consequences of prog- 

 ress, or evolution, iu human society. For 

 some purposes it would have been wise to 

 give each part a distinct title, reserving for 

 the last part the one used ; but the philo- 

 sophic system propounded in the first part has 

 evidently been prepared as a basis for the 

 second, and in itself would not be considered 

 by the author as a complete exhibit of his 

 philosoph}-. 



Vol. i. contains : first, an outline of the 

 work, in which the author's purposes are 

 clearly set fortli ; second, an liistorical review, 

 chiefly devoted to a discussion of the philoso- 

 phies of August Comte and Herbert Spencer ; 

 third, the cosmic principles iiudeiiying social 

 phenomena, in which the outlines of the new 

 system are set forth. Under the general title 

 of "primary aggregation,' he discusses the 

 constitution of celestial bodies and chemical 

 relations. Under that of ' secondary aggrega- 

 tion,' he discusses biology, psycholog3'. and 

 the genesis of man. Under that of ' tertiary 

 aggregation,' he discusses the genesis of so- 

 ciety and the characteristics of soci.il organiza- 

 tion. The purpose of this preliminary volume 

 on general ijiiilosophy, and of the introduction 

 to the second volume, is tersely given by Mr. 

 AVard himself, as follows : — 



"The purpose of the present chapter 

 [chap, viii.], as already announced, has been 

 to accomplish the complete orientation of 



