Chemistry and Physics. 401 



Designation of tfae mass system, by L. Pfaundler. 



On a new form of galvanic battery, by F. Friedeichs. By an 

 attachment similar to the mercury vessel employed in the Toepler 

 air pump, the author regulates the height of liquid in a series of 

 galvanic cells. j. t. 



14. On PritcharcPs Wedge Photometer* — The photometer de- 

 vised by Professor Pritchard, consists of a wedge of neutral 

 glass which is inserted between the observer's eye and the eye 

 piece of the telescope and moved along until the thickness is 

 sufficient to render a given star invisible. An instrument of this 

 kind has been successfully used in obtaining the measures of the 

 light of the stars given in the Uranometria Oxoniensis. In 

 order to test its value and accuracy some observations have been 

 recently made by Professors Young, Langley and Pickering. 

 The former makes some practical remarks in regard to the ease 

 and convenience of its use based upon the results obtained upon 

 six stars in the neighborhood of y Pegasi and gives, estimates of 

 the probable error in the determination of magnitude. He states 

 that the method is much more wearisome to the eye than those 

 involving the equalization of the light as in the double image 

 photometers. 



Professor Langley investigated the wedge by means of the 

 bolometer and found that there was a distinct selective absorp- 

 tion throughout the wedge, even in the visible rays ; this was 

 feeble in the more luminous part of the spectrum but such that 

 the transmissibility increased from the violet toward the red, and 

 still more beyond the red. In order to decide the question as to 

 the influence of this selective absorption upon the value of the 

 instrument for photometric work, Professor Pickering made a 

 series of measurements with it at the Harvard Observatory and 

 added to these some photographs of the solar spectrum through 

 it. The photometric measures failed to show the gradual diminu- 

 tion in the coefficient of absorption as the thickness increased. 

 The photographs, however, showed that the intensity of the 

 spectrum transmitted fell off rapidly, beyond A = # 41 becoming 

 entirely invisible at A = 040. The opacity of the wedge increased 

 rapidly as the wave-length diminishes, as the bolometer showed. 

 The conclusion is reached that, though valuable results may be 

 obtained by the wedge photometer when skillfully used, the ob- 

 servations show sources of error needing careful study before it 

 can safely be applied to stars of different colors, or to detecting 

 small systematic errors in the star catalogues. 



15. n the Beneficial Effects of Light ; by Gr. G. Stokes. 100 

 pp. 12mo. London and New York, 1887. (Macmillan & Co.). — 

 This volume contains four lectures delivered as the third course 

 of Burnett lectures at Aberdeen in November, 1885. They deal 

 with topics which are readily understood and are presented in a 

 simple and agreeable style. They will be enjoyed now in perma- 

 nent form by a larger audience than that before which they were 

 presented. 



* Investigations on Light and Heat, published with appropriation from the 

 Ruinford Fund. 



