,706 REPORT— 1893. 



11. On Electro-magnetic Trails of Images in Plane, Spherical, and 

 Cylindrical Current Sheets. Bij G. H. Bryan, M.A. 



The problem of electro-magnetic induction in spherical and ellipsoidal current 

 sheets has been dealt with by Professor N iven, Dr. Larmor, Professor Horace Lamb, 

 and other writers, but, so far as the author is aware, no attempt has been made to 

 apply the method of images to current sheets except in the well-known case of an 

 infinite plane sheet, so fully treated by Maxwell and other writers. The author 

 has worked out the images of a fixed magnetic pole of variable intensity in 

 presence of a spherical current sheet, and has performed the corresponding investi- 

 gation for the cylinder under the influence of a line distribution of magnetism of 

 variable intensity parallel to the axis of the cylinder, the problem being in this 

 case two dimensional. From the results thus obtained the images of a moving 

 pole may be constructed in the same manner as for a plane sheet. In the particular 

 case of a pole revolving outside a spherical shell about its centre, the images which 

 determine the magnetic potential at any point inside the shell lie on an equiangular 

 spiral. 



12. On Thermal Relations hetiveen Air and Water. 

 Bij Hugh Robert Mill, D.Sc, F.B.S.E. 



The conclusions stated in this paper were deduced mainly from the author's 

 observations on the Clyde Sea Area. The physical character of the Clyde Sea 

 Area depends mainly on the form of the hollows of which it is composed and 

 the degree of isolation of each from oceanic influences. The North Channel between 

 Scotland and Ireland was found always in a homothermic condition, i.e., the tem- 

 perature was the same from surface to bottom, an effect traced to the tidal mixing 

 of the water. The Channel water was on the average of the whole year 1°'7 F., 

 warmer than the air at the Mull of Cantyre. The air reached its maximum in the 

 end of July, the water not until the middle of September. Up to that date the 

 air was warmer, but from September to April the water was warmer. On the 

 plateau or broad shallow stretching across the mouth of the Sea Area from 

 Cantyre to Galloway the water was usually highly heterothermic, i.e., the tempera- 

 ture varied greatly from surface to bottom. Only at the period of the annual 

 minimum was the temperature uniform throughout. On the plateau the Channel 

 water mixed with that of the great Arran basin, the deepest and most open of the 

 natural divisions of the Clyde Sea Area. In the Arran basin the water was homo- 

 thermic throughout at each spring minimum about the month of March, and as 

 heat was being stored or lost the lower layers remained homothermic, becoming 

 least so about the time of the autumn maximum. The surface layers heated up 

 most rapidly, and cooled down most rapidly, but the average temperature of the 

 whole mass of water was always lower than that of the Channel, except for about 

 a month at the spring minimum. The maximum temperature of the mass also was 

 retarded to the middle of October, up to which date the water as a whole was 

 colder than the air, but after that date was warmer till the spring minimum. The 

 condition of things in the more isolated barred off' sea lochs, such as Loch Fyne 

 and Loch Goil, showed still more strongly the effects of isolation from oceanic 

 influence. The mass of the water in Loch Fyne, although nearly of the same 

 temperature as the other divisions about the period of minimum, was much colder 

 during the rest of the A^ear than that of the Arran basin, which in turn was colder 

 than the Channel. The date of maximum temperature was a few weeks later than 

 that of the Arran basin, and at least three months later than that of the air. The 

 diflference between the behaviour of the surface and bottom water with regard to 

 temperature became more and more marked with the degree of isolation from 

 oceanic water. In Loch Fyne and Loch Goil the warmth of summer did not affect 

 the bottom water for about six months, and the greatest cold of winter took about 

 three months to make itself felt at the bottom. 



