Chemistry and Physics. 285 



late the means for any one observatory. The mean intensities of 

 radiation have been investigated for 18 wave-lengths comprised 

 between, and inclusive of, the limits 0-30 /*, and 2*50 //,. The solar 

 energy-spectrum is plotted together with the theoretical curves 

 for a black body at temperatures of 6200° and 7000° absolute 

 Centigrade. For the adopted mean spectrum-energy-curve the 

 maximum of energy falls at 0*470 /x. 



Using the Wien displacement formula, A. n ,T = 2930 (A m = 0*470^), 

 the effective solar temperature is found to be 6230° absolute Cen- 

 tigrade. If, on the other hand, the Stefan formula for total radi- 

 ation, E=76'8XlO~ 12 T 4 , be employed, the aforesaid temperature 

 comes out 5830° absolute. (In making this calculation Abbot 

 uses the following numbers : solar radius = 696 X 10 3 km, mean 

 radius of earth's orbit =: 14,956 X 10 4 km, and the solar constant = 

 1*922 calories per cm* per min.) In his summary Abbot says : 

 " The conclusion is drawn from the observations cited that the 

 sun's emission approximates roughly to that of a " black-body" at 

 6000° absolute Centigrade, but that on account of influences prob- 

 ably active, we ought to assign a solar radiating temperature of 

 the order of 7000° absolute Centigrade." The discussion by 

 Abbot of these probable sources of error is too long to be repro- 

 duced here ; suffice it to say that, in general, these influences 

 would lead us to too low a value for the mean solar temperature. 

 — Astrophys. Jour., vol. xxxiv, Oct. 1911, p. 197. h. s. it. 



12. College Physics ; by John Oren Reed and Karl Eugen 

 Guthe. Pp. xxviii, 622. New York, 1911 (The Macmillan Co.). 

 — Since the authors have deemed it wise to present the chief divi- 

 sions of the subject in a rather unusual sequence, it seems fair 

 and pertinent to make the following quotation from their preface. 

 "Owing to the more obvious relations existing between them, the 

 subject of heat is made to follow immediately after the distinctly 

 material phenomena of mechanics and sound ; electricity precedes 

 light, and the subject of radiation, usually found under the differ- 

 ent chapters of heat, electricity and light, is treated separately 

 after these subjects have been presented." "It has also been 

 thought best, even at the sacrifice of historical consistency, to 

 begin the subject of electricity with current electricity, in order 

 to secure the advantage of the greater familiarity of the student 

 with the phenomena of applied electricity." 



Certain other salient features of the book merit enumeration. 

 References are frequently made, by means of unobtrusive foot- 

 notes, to the laboratory experiments described in Reed and 

 Guthe's "Manual of Physical Measurements," (3d edition, George 

 Wahr, Ann Arbor.) Numerous references to original papers 

 are also made in the foot-notes, to the end that the student may 

 acquire interest both in the historical and critical aspects of 

 scientific investigation. Several of these references presuppose a 

 reading knowledge of scientific German. The text assumes an 

 acquaintance, on the part of the student, with a few formulae 

 of plane trigonometry and with the calculus notation of deriva- 



