40 REPORT — 1873. 



On a curious Phenomenon ohserved on the top of Snowdon. 

 By Akthtjr Schtjstee, Ph.D. 



Tliis was a sliort account of a curious phenomenon observed by the author two 

 years ago on the top of Snowdon. He saw his own shadow surrounded by five 

 concentric coloured bows, which seemed to approach as the fog came nearer, until 

 at last he saw the shadow of his head surrounded by a brilliantly coloured ring. 

 Similar phenomena have often been observed ; but so great a number of bows has 

 never been seen. 



Heat. 

 On Thermal Conductivity. By Prof. G. Forbes. 



Notes of some Expenments on tlie Thermal Conductivities of certain Hocks. 

 By Prof. A. S. Herschel, B.A.,F.R.A.S. 



The paper read was an abstract of the physical portion of that communicated to 

 the Geological Section by Professor Herschel and Mr. G. A. Lebour. It was re- 

 marked that the principal difficulty in determining thermal conductivities from 

 experiments with thin plates, is to ascertain the real temperatures of their faces 

 during the transmission of the heat. The measurements of temperature were 

 made with thermoelectric couples of tbin platinum and iron wires connected with 

 a Thomson's reflecting galvanometer ; and it was found that although enclosed 

 between two metallic plates differing as much as 80° or 90° C. from each other 

 in temperature, the corresponding range of temperature between the two surfaces 

 of the half-inch rock plates employed in the experiments only amounted at most 

 to between 3° and o° C, while the amount of heat transmitted with this range 

 corresponded very nearly to the approximately known thermal conductivities of 

 the rocks. The thermal resistance between the surfaces of solid conductors and 

 air or other fluids in which they are immersed having been shown by Peclet to 

 arise from an adhering film of the badl}' conducting fluid with which they are in 

 contact, it is proposed in another series of experiments, by varying the thicknesses 

 of the conducting plates, to ascertain the laws of this resistance, and, if they admit of 

 a convenient interpretation, to an-ive at some simple means of eliminating the effects 

 of its influence upon the calculated results of experiments like those to which the 

 various rock-specimens now examined have hitherto been provisionally submitted, 

 and to obtain exact determinations of their real powers of conducting heat. 



On the Correlation hetween Specijtc Weight and Specific Heat of Chemiccd 

 Elements. By Prof. Zengee. 



Electricitx and Magnetism. 



On the Molecidar Changes that accompany the Magnetization of Iron, Nichel, 

 and Cobalt. By W. F. Barrett. 



On the Eelationship of the Magnetic Metals, Iron, Nickel, and Cobalt. 



By W. P. Barrett*. 



* See the Philosophical Magazine for December 187o, p. 478. 



