654 report — 1884. 



10. On the Velocity of Light in Oarbon Bisulphide and the Difference in 

 Velocity of Bed and Blue Light in the same. By Albert A. Michelson. 



The arrangement of apparatus was essentially the same as in the experiments of 

 Foucault. The liquid was contained in a tube 2 feet long, with plate-glass ends. 

 With about 300 turns per second, and a radius of 20 feet, a deflection of 1^ mm. 

 was obtained. 



The principal difficulty was the obtaining a clear image through the liquid. 



The ratio of the velocity in the liquid to that in air was found to be as one to 

 T75. The theoretical value is the refractive index of the liquid, or 1*65. 



In the second part of the work the light was coloured by a direct-vision prism 

 placed before the slit. The colours selected were half way between C and D and 

 half way between b and F. 



It was found that the red ray travelled 2i per cent, faster than the blue, which 

 is in accord with theory. 



11. On a Systematic Research for Stars with a Measurable Annual Parallax, 



and its Results. By Professor Robert S. Ball, LL.D., F.R.S. 



12. On an Electrodynamometer, with extremely light moving coil, for the 

 'measurement of small alternating currents. 1 By Dr. W. H. Stone. 



The moving coil is made of aluminium wire, which for given mass conducts 

 better than any known substance. This is silk-covered, and wound in an anchor- 

 rinw-shaped form on a hollow bobbin of cork. The two ends are brought up to a 

 small plate of ebonite, and connection is perfectly made by means of minute 

 clamping screws, with a bifilar suspension of gilt silver wire. The bobbin is then 

 immersed in a small tank of petroleum oil, which serves at once (1 ) to lessen its 

 weight, (2) to act as a preserver of the insulation, and (3) to damp any excessive 

 vibration. 



The instrument has the great additional advantage of moving quickly up to its 

 full deflection, and thus giving less time for the running down of the battery 

 attached to the primary inducing coil than that which occurs in the ordinary form 

 of the instrument. As cork swims in heavy petroleum lamp oil, and the silk- 

 covered aluminium wire sinks, a combination of the two of any given specific 

 gravity within certain limits can easily be obtained. (See ' Nature,' Oct. 30, 1884.) 



13. On the Law regulating the Connection between Current and Intensity 

 of Incandescence of Carbon Filaments in Gloiv Lamps. By W. H. 



PREECE, F.R.S. 



In a paper read before the Royal Society in 1883, I pointed out, from experi- 

 mental data, that the light emitted by a glow lamp varied apparently as the sixth 

 power of the current. 



I have verified this law, not only by subsequent experiments of my own, but, 

 •which is much more satisfactory, by experiments of others. Professor Battler, of 

 Darmstadt, and Captain Abney have made, independently of each other, most 

 careful and exhaustive measurements in this direction. I have tabulated and 

 traced them out in curves, which I submit. They fully confirm the law that 



L = kC* 



but within limits, and that these limits embrace the ordinary range of a glow lamp 

 when used for artificial illumination. As long as the resistance and the current 

 vary uniformly together, the law holds good ; but as the state of incandescence is 

 increased, a point is reached, varying with each kind of lamp, when the resistance 

 ceases to diminish at the same rate, and eventually to increase. When this occurs 

 the law is departed from, and the light emitted increases much faster than the 



1 £ee Nature, October 30, 1881. 



