TRANSACTIONS OF THE SECTIONS. 



Specific Magnetism. 



Intensity of the current Intensity of the current 



= 1. =4. 



Iron 1000000 1000000 



Cobalt 1008900 912200 



Nickel 465700 350900 



Oxideofiron 758 954 



Oxide of nickel 286 405 



Hydrate of oxide of cobalt 2178 5015 



Bismuth 23-6 39-03 



Phosphorus 16-45 27-31 



On a New Photometer. By Astley Paston Price, Ph.D., F.C.S. 



The object sought in this modification of the Photometer is the combination of 

 the two images usually obtained when estimating the difference of intensity' between 

 two sources of illumination, and by so doing facilitating the valuation of the difference 

 betweeen the light to be determined and a recognized standard. 



The Photometer is so constructed that the rays of light, after passing through 

 orifices at either side of the instrument, impinge on two mirrors placed at an angle 

 of 45° ; by such an arrangement, when an observation is made the two images are 

 united, which facilitates the comparison and permits the more easy approximation 

 to neutrality. 



The orifices may be of any desired form ; those which have been adopted are either 

 oblong apertures covered with tissue paper, placed, on the one side horizontally, and 

 on the other perpendicularly, or two semicircular discs may be substituted ; in the 

 former case the two are united and crossed at right angles, and in the latter a circu- 

 lar disc is obtained. It is obvious that any design may be adopted, the object being 

 that the resulting combination shall afford facility of comparison. 



General View of an Oscillatory Theory of Light. 

 By W. J. Macquorn Rankine, C.E., F.R-S.S. Loud, and Edin. 



The author endeavours, while retaining the whole of the mathematical forms of 

 the undulatory theory of light, to render the physical hypothesis which serves as its 

 basis more consistent with itself and with the known properties of matter. Light, 

 according to the undulatory theory in its most general sense, consists in the propa- 

 gation of some species of motion amongst the particles of the luminiferous medium, 

 the nature and magnitude of which motion are functions of the direction and length 

 of certain lines transverse to the direction of propagation. According to the existing 

 hypothesis of vibrations, this motion is a vibration of the atoms of the luminiferous 

 medium in a plane transverse to the direction of propagation. In order to transmit 

 motions of this kind, the parts of the luminiferous medium must resist compression 

 and distortion, like those of an elastic solid body ; its transverse elasticity being 

 great enough to transmit one of the most powerful kinds of physical energy with a 

 speed in comparison with which that of the swiftest planets of our system is appre- 

 ciable, but no more, and its longitudinal elasticity immensely greater ; both these 

 elasticities being at the same time so weak as to offer no perceptible resistance to the 

 motion of the planets and other visible bodies. The author considers that it is 

 impossible to admit this hypothesis as a physical reality. He also points out the 

 difficulties arising from certain inconsistencies in the present theory as to the rela- 

 tion of the direction of vibration in polarized light to the plane of polarization. 



The author then proposes what he calls the hypothesis of oscillations, which con- 

 sists mainly in conceiving that the luminiferous medium is composed of detached atoms 

 or nuclei, distributed throughout all space, more or less loaded with atmopheres of 

 ordinary matter, and endowed with a species of polarity, in virtue of which three 

 orthogonal axes in each atom tend to place themselves parallel respectively to the 

 three corresponding axes in every other atom ; and that plane-polarized light con- 

 sists in a small oscillatory movement of each atom round an axis transverse to the 

 direction of propagation, and perpendicular to the plane of polarization. The square 



