358 RECORD OF SCIENCE FOR 1886 



beams traverse a nicol, then a rboinbohedrou of spar cut of such a 

 thickness that the ordinary ray from one of the sources of light and the 

 extraordinary ray from the other issue juxtaposed. The two beams are 

 received by a telescope, having previously been equalized in intensity 

 by rotating the nicol. From this rotation the original intensities are 

 calculated. The results of measurements thus made confirmed very 

 closely the law of the cosines, and also showed that the amount of emit- 

 ted energy polarized perpendicular to the plane of incidence increases 

 rapidly with the obliquity. (Wied. Ann., xxiv, 26G; J. Phys., No- 

 vember, 1886, II, V, 574.) 



Mercadier has divided radiophones into two classes: (1) those in which 

 the transformation of radiant energy into mechanical energy in the 

 form of sound is produced directly, and (2) those in which this trans- 

 formation of energy is effected indirectly through one or more interme- 

 diate stages. The original photophone of Bell, in which the intermittent 

 beam fell on selenium, and thus affected an electric circuit in which a 

 telephone was placed, was of the latter class. The author has observed 

 that if a beam of intermittent radiations be allowed to fall upon the di- 

 aphragm of a microphone, the corresponding note is distinctly heard in 

 a telephone in circuit with it; and further, such a beam is capable of 

 producing the same effect when thrown on the diaphragm of a magneto 

 transmitting telephone. (J. Phys., May, 1886; II, v, 215.) 



Langley has continued his researches on radiant energy and has now 

 published his observations on invisible heat spectra and the recognition 

 of hitherto unmeasured wave lengths. As radiating surfaces Leslie 

 cubes were employed, covered with lampblack and filled with boiling 

 water giving 100°, or aniline giving 178°. In some cases the cubes were 

 filled with ice, and even with freezing mixtures, at a temperature of 

 —20°. The apparatus consisted of a rock salt train, made up of two 

 rock salt lenses 75""" diameter and 350'""' focus, and a rock salt prism 

 64™™ on a side. The conclusions reached from an examination of the 

 curves are (1), that the heat now measured is almost altogether of a char- 

 acter not observed in that of the sun, the wave lengths not being trans 

 missibleby glass; (2) that notwithstanding the compression of the in- 

 fra-red by the prism, these heat curves extend almost indefinitely in that 

 direction, the Leslie cube, for instance, at 178°, showing very measurable 

 heat at adeviation of 33°, corresponding to a retractive index of 1.4511; 



(3) that an increase of temperature increases every ordinate, but not 

 equally, those in the more refrangible portions growing most rapidly; 



(4) that hence there is a progressive movement of the maximum ordinate 

 toward the more refrangible end as the temperature rises ; and (5) that 

 these prismatic curves are not symmetrical, the greater portion of the 

 area in erery case lying toward the greater wave length. In one of the 

 plates accompanying the paper the curves of two heat spectra are given, 

 one from a surface at the temperature of boiling water, the other at that 

 of melting ice. As first approximations, the author believes that " the 



