INDUSTRIAL PROGRESS DURING THE YEAR 1874. xliii 



of a phosphatic glass containing a suitable percentage of 

 titanic acid. Cornu explains a mode of constructing for as- 

 tronomical photography a lens whose focal length shall be 

 the same for both chemical and visual rays. His method 

 differs but little from that originally used by Rutherford, but 

 subsequently improved upon by him. 



Hirn and others, from observations on the reflection of 

 sunlight from a sheet of flame, show that probably the glow- 

 ing solid particles that give the flame its brightness are 

 themselves at the same time nearly transparent. The inter- 

 esting researches of Wiedemann into the superficial colors 

 of bodies have shown that the problem depends on the con- 

 nection between absorption and elliptic polarization. 



The introduction of diffraction gratings, instead of prisms, 

 in spectroscopic research continually extends; and, according 

 to the experiments of Rayleigh, these fine-ruled plates may 

 be reproduced by the photographic process of contact print- 

 ing. He has also published a well-timed essay on the the- 

 ory of the action of gratings, which leaves nothing to be de- 

 sired. 



Mr. J. M. Blake has applied a very ingenious method of 

 testing the accuracy of diffraction gratings by superposing 

 the lines of the gratings, and observing the appearances 

 produced by the crossing of these lines. In these positions 

 the lines produce effects similar to those observed when we 

 view one picket-fence through another. 



In Electricity, Professor Mayer has quite recently succeed- 

 ed in analyzing the composite phenomenon of the electric dis- 

 charge, by passing the flashes of various electric discharges 

 through rapidly revolving disks of thin paper coated with 

 the smoke of burning camphor. By these simple means he 

 has arrived at the most remarkable results, especially in the 

 case of a large induction coil, whose discharge, when a small 

 Leyden jar is in its circuit, he finds to consist of between 90 

 and 100 distinct flashes, gradually closing up on each other 

 in the middle of the discharge, where they succeed each 

 other at each 10< 1 000 of a second, and again separating to- 

 ward the end of the discharge. 



The formation of the American Electrical Society (of which 

 Anson Stager is president) will, we hope, stimulate original 

 research as well as "practical" work in this field. Messrs. 



