598 SCIENTIFIC RECORD FOR 1883. 



space being 1, that inside matter is called K, the specific inductive 

 capacity, while in optics it was measured by the square of the refractive 

 index. These appear to be the same values. The vortex atom theory 

 of Thomson is discussed, and the lecture closes as follows: "One con- 

 tinuous substance filling all space, which can vibrate as light, which can 

 be sheared into positive and negative electricity, which in whirls con- 

 stitutes matter, and which transmits by continuity and not by impact 

 every action and reaction of which matter is capable. This is the 

 modern view of the ether and its functions." {Nature, January arid 

 February, 1883, xxvn, 304, 328.) 



Preece has proposed to the Royal Society the use as a reference photo- 

 metric standard a small surface illuminated to a given intensity. In 

 practice the light given by a small incandescent lamp, which can be 

 varied by varying the current, is used for the comparison. The amount 

 of illumination is proportional to the current flowing, and is read in 

 amperes. The standard surface is that illuminated by a British candle 

 at 12.7 inches, the same as is given by the French carcel at 1 meter 

 distance. The theory of the method is simple. {Nature, June, 1883, 

 xxvm, 206.) 



Sabine has described a wedge and diaphragm photometer which 

 consists of a horizontal brass tube on a stand having an eye-piece at 

 one end and a paraffin lamp at the other. A disk of opal glass near 

 the middle of the tube is constantly illuminated by the flame. The 

 tube itself is cut away laterally near its center, the opening being cov- 

 ered by a collar carrying a slit containing a strip of opal glass, before 

 which slides a frame carrying a wedge of neutral-tint glass, the thicker 

 end of which absorbs eight times as much light as the thin end. The 

 light to be measured is placed on the right side of the photometer, and 

 its rays pass through the wedge and slit, falling on a narrow mirror at 

 45°, which reflects them to the eye. When the light from the paraffin 

 lamp and that from the source under examination are balanced the 

 mirror becomes invisible. Diaphragms, with various openings, placed 

 at the lamp end of the tube, permit the range to be varied. {Phil. May., 

 January, 1883, V, xv, 22.) 



Conroy has suggested a modification of Eitchie's photometer in which 

 two surfaces of white paper are so placed that the light is incident 

 upon them at 30°, and the line of sight makes an angle of 00° with the 

 normal, one of the papers being made to overlap the other slightly. 

 {Phil Mag., June, 1883, V, xv, 423.) 



Sir William Thomson has made some approximate photometric meas- 

 urements of natural as compared with artificial lights. From Pouillet's 

 data he estimates the solar radiation to be 7,000 horse-powers per square 

 foot of the sun's surface, or 50 horsepowers to the square inch. The 

 radiation from a Swan incandescent lamp he finds to be three-fourths 

 of a horse-power per square inch of surface, and hence the sun's radia- 

 tion is 07 times that of the lamp. From measurements taken at York 



