292 Scientific Intelligence. 



also Y (8986) and Y (8990) are not telluric lines but belong, 

 according to the author, to metals with low melting points. The 

 catalogue of lines given by Abney includes 590 lines. — Beiblat- 

 ter, Ann. der JPhysik, No. 5, 1888, p. 351. j. t. 



2. Photometry of Color. — A communication on this subject 

 was read to the Physical Society, June 23, by Captain Abxet. 

 The apparatus consisted of a spectroscope and camera similar to 

 those used by the author for the production of monochromatic 

 light. A small shadow photometer served for the measurement. 

 The screen was made of two parts — one the color to be tested 

 and the other white or black according to the standard employed. 

 The stick was arranged so that the shadows fell near the junction 

 of the two parts. Light reflected from the surface of the first 

 glass prism served to illuminate one shadow; and for the other, 

 monochromatic light of any desired color could be used. The 

 intensities were adjusted to equality by cutting off more or less 

 of the stronger light by means of a revolving wheel with adjust- 

 able sectors, the opening of the sectors being a measure of the 

 luminosity of the pigment. In another arrangement a double 

 image prism was used to separate the spectrum into two parts. 

 Monochromatic light from one part passed direct to the screen 

 through sectors in a rotating wheel, and monochromatic light 

 from the other spectrum was reflected on the screen at a sufficient 

 azimuth to give a separate shadow, by means of two total reflec- 

 tion prisms. The losses by reflection were allowed for by obtain- 

 ing the position of the adjustable sectors required to give equal 

 intensities on a white screen. From the results color curves can 

 be plotted for different pigments and templates constructed 

 which, when rotated in the path of the spectrum, reproduce the 

 corresponding color. In the course of the experiments many in- 

 teresting observations on color blindness were obtained. Colors 

 could be imitated whatever the source used to produce the spec- 

 trum.— Nature, July 19, 1888, p. 286. j. t. 



3. Heat Measurement. — At a meeting of the Physical Society, 

 Berlin, Dr. P. vox Helmholtz exhibited a new form of bolometer, 

 differing from that used by Langley. In the latter's instrument 

 the alterations of electrical resistance produced by radiation are 

 measured by introducing the exposed bolometer into one arm of 

 a Wheatstone's bridge, a similar one protected from the light 

 being introduced into the second arm of the bridge, while the 

 other two arms contain a corresponding resistance. In the new 

 bolometer constructed by Siemens and Halske all four arms of 

 the bridge are composed of equal wires rolled up into a coil and 

 of these coils 1 and 3 are illuminated, while 2 and 4 are protected, 

 and then 2 and 4 are illuminated and 1 and 4 protected. By 

 this means a four-fold sensitiveness is theoretically obtained. 

 All four coils lie inside a brass tube, and by turning a screw, at 

 one turn coils 1 and 3, at another, 2 and 4 are brought opposite 

 the opening. Langley's results appear to be five times more deli- 

 cate than those of the author. This is due to Langley's galvano- 



