30 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



logues of two American makers, Buff and Berger, of Boston, 

 and Fauth and Co., of Washington, arc notewortliy in this 

 connection. The latter firm lias lately proposed to make a 

 transit-circle for Princeton College, which, when completed, 

 will be the first meridian instrument of large size made in 

 the United States. A transit instrument for the same col- 

 lege lias been completed by Kahler of Washington. 



The 18-inch refractor for Strasburg has had several objec- 

 tives made for it by Merz, among which a choice must yet 

 be made, and until then work on the mounting is stopped. 



Grubb, of Dublin, has just completed two 8-J-inch equa- 

 torials for Berlin and Dresden, in which he has incorporated 

 his latest improvements with regard to illumination of 

 field, wires, etc. One reading microscope suffices to read 

 both declination and rioht-ascension circles. 



CD 



The Naval Observatory of Washington has recently pub- 

 lished a description of its principal instruments, with plates. 

 It is Appendix I. to the Observations for 1874. 



Titano-silicic glass prisms have been examined by Pro- 

 fessor Stokes and Dr. Hopkinson, and the hopes that had 

 been entertained of the utility of this glass in the correc- 

 tion of the secondary spectrum were not fulfilled. The 

 phosphatic glass of Ilarcourt, while a success in this respect, 

 is too soft for use in optical glass, and the new glass, in 

 which a portion of the phosphorus was replaced by tita- 

 nium, would have been suitable in this respect. The ques- 

 tion is, then, as far from a practical solution as ever. 



Experiments on the electro-static capacity of glass did 

 not bear out Maxwell's conclusion as to the relation be- 

 tween the refractive index for long waves, the electro-static 

 capacity, and the magnetic permeability. 



The paper on the refractive indices of glass refers mostly 

 to glasses which are articles of commerce, and hence is of 

 immediate value. Specimens of hard crown, soft crown, 

 titano-silicic crown, extra light flint, light flint and dense 

 Hint, extra dense flint, and double extra dense flint were 

 examined, and an expression for the irrationality of dis- 

 persion of each of these glasses compared with a stand- 

 ard is obtained and tabulated. This table shows how 

 little there is to choose between the glasses ordinarily 

 used. 



