January 2, 1914] 



SCIENCE 



27 



picture. The silvering process was evidently 

 described during a moment of relaxation 

 when the author's characteristic humor came 

 to the surface as follows : " Personally I never 

 weigh my nitrate of silver, as I enjoy the ele- 

 ment of the personal equation which enters 

 the problem when scales are dispensed with." 

 How seriously this is to be taken may be 

 judged from one or two of his immediately 

 following sentences. " From one to two grams 

 to 100 e.c. of distilled water is about right." 

 " Unfortunately things as described above 

 seldom happen at the first trial." " It troubled 

 me much when my personal equation con- 

 tained one more variable than at present, but 

 I have not seen it occur recently. As the 

 production of the uniform blue film depends 

 upon getting the proportions just right, I sup- 

 pose the beginner had better mix measured 

 amounts for each trial unless he has access to 

 a large jar of silver nitrate which ' belongs to 

 the department.' " " The cause of this I do 

 not know. Probably it is osmotic or perhaps 

 catalytic ! " 



The results contained in the next paper, 

 entitled, " Note on the electron atmospheres 

 of metals," are capable of a quite different and 

 less significant interpretation than that given 

 by the author, as has already been pointed out 

 by several other investigators. 



The resolution of the four principal mer- 

 cury lines, by a five-inch plane grating, ruled 

 by Anderson at Baltimore, is discussed in 

 Paper No. 10, and speaks well for the high 

 quality of the grating. 



The eleventh paper concludes the series 

 with an interesting explanation and experi- 

 mental verification of the " Imprisonment of 

 Radiations by Total Reflection." 



Of the volume as a whole, one hardly knows 

 whether to admire more the boldness of ideas 

 which prompt the experiments or the manipu- 

 lative skill with which they are executed. 

 Henry Crew 



noethwesteen university 



Astronomy: A Popular Handbooh. By 

 Harold Jacoby, Rutherford Professor of 

 Astronomy in Columbia University. The 

 Macmillan Company, New York. 1913. 



Most astronomers yield at one time or an- 

 other to the desire to write some popular trea- 

 tise on astronomy. Professor Jacoby has pre- 

 pared his volume in the effort " to meet the 

 wishes of the ordinary reader who may desire 

 to inform himself as to the present state of 

 astronomical science, etc." The book is in- 

 tended also to serve for use in high schools 

 and colleges. To meet this double end, the 

 author has placed all the mathematical notes 

 and explanations in the appendix, where they 

 are at the service of students, while the main 

 body of the text is free from mathematics, 

 which might discourage the " ordinary reader." 

 This method of arrangement is not unusual, 

 but the author has carried it out more syste- 

 matically than is usually done. 



Professor Jacoby's treatment of the subject 

 is distinctly out of the ordinary, and it is 

 this originality of method and style which may 

 well furnish the raison d' etre for this addition 

 to our astronomical literature. The first chap- 

 ter is in the form of a general survey of the 

 universe, a prelude to the detailed descriptions 

 which follow. In the third chapter methods 

 are given for finding the planets and stars. 

 This chapter, however interesting for other 

 reasons or valuable for intellectual training, 

 does not impress one as containing the simplest 

 methods for gaining familiarity with the stars 

 and planets. Monthly maps are now pub- 

 lished giving the appearance and positions of 

 planets and comets as well as the stars, and it 

 is doubtful if any verbal description, tables and 

 small diagrams can compare in efiiciency with 

 such maps in assisting an ordinary reader to 

 the identification of celestial objects. The 

 author, however, would doubtless encourage 

 the use of such maps in connection with the 

 reading of the book. Chapter V. gives a brief 

 but admirable discussion of the sun dial with 

 a description of the manner in which one may 

 be constructed by the reader. The earth and 

 its relationships are handled in an original and 

 interesting way. Under " Moonshine " the 

 author presents the leading facts about our 

 satellite, giving the usual proof of the absence 

 of an atmosphere and the probable cause of its 

 disappearance. No reference is made to the 



