644 ■ • report — 1884. 



16. On the Formation of Frasil Ice. By G. H. Henshaw. 



The author suggests the theory that ' frasil ice ' is a true growth upon substances 

 beneath the surface of the water, due to the refrigeration of these nuclei by cold 

 currents, in contradistinction to the theory that this ice is first formed on the 

 surface, and afterwards carried down by currents and attached by a process of 

 regulation to substances at the bottom. 



17. Note on the Internal Temperature of the Earth at Westville, 

 Nora Scotia. By H. S. Poole, F.G.S. 



On the slope or incline of the Acadia colliery in the Picton coalfield, reaching 

 a length of 2,350 feet, at a depth of 900 feet below the outlet, holes were bored in 

 the freshly mined coal, thermometers inserted, the openings closed, and the 

 temperature taken after some hours. The experiment was repeated, and the record 

 of 55° Fahr. verified. 



The ground immediately over the experimental station falls away with the dip 

 of the measures, and is at that point about 930 feet in thickness : taking this as 

 the depth, and allowing for the depth at which the mean surface temperature 

 (42° Fahr.) is uniform by adding 1 to 13 (the difference iu degrees between the 

 surface mean temperature and that observed in the coal at the bottom of the incline), 

 the number 14 is divided into 930, the depth, and the result obtained is an average 

 depths of 66 feet for each degree in temperature. 



The practical interest attached to such an experiment lies in connection with 

 the depth at which in the future coal may be mined in Nova Scotia without 

 inconvenience from high temperature. 



The initial mean temperature being 9° (?) below that of the North of England, is, 

 according to this experiment, equal to a depth of 600 feet greater than in England 

 before a corresponding temperature is reached. 



So far as is at present known, it is probable that seams of workable thickness 

 in the Picton field lie at a depth of 4,000 feet; in the Cumberland field at still 

 greater depth ; and in Cape Breton, where the seams dip under the ocean, there is 

 every reason to believe they extend to great distances and depths. 



In the author's report as Inspector of Mines, in 1877, he referred to the value 

 of these submarine fields, and to the necessity for care in working in our own day 

 the out-crops of the seams near the shore, in order that the wealth seaward may be 

 secured for our successors. 



18. On the Formation, of Mackerel Sky. By Dr. H. Motrhead. 



At the Glasgow meeting of the Association in 1876, Sir William Thomson read 

 a short note on the formation of mackerel sky. The author having paid much 

 attention to the various aspects of the congeries of cloudlets so named, has come 

 to the conclusion that the following is the usual mode in which they are generated. 

 Given a thinnish stratum of air moist in process of passing over a drier and cooler 

 body of air, of different velocity or direction. The vapour by cooling will become 

 visible, and from friction the stratum will get rolled into long cylinders. Now let 

 another current of air brush across the cylinders at right angles to their length, or 

 indeed any large angle. This will have the effect of rolling the thinnish stratum 

 into cylinders crossing the first set. And now neither set will appear as long con- 

 tinuous rollers, but from being crossed will show as a coDgeries of little cloudlets 

 or drums, i.e., mackerel sky. 



In favour of this hypothesis it may be noted that if attention be paid to the 

 cloudlets there will often be observed, at one or other extremity of the formation, 

 portions of the cylinders which extend continuously for a considerable length 

 where they have not been divided into drums by a crossing current. Again, if one 

 of the currents moves too rapidly, some of the cloudlets will get so torn by it that 

 they will often show as wisps or mare's tails. Moreover, it may sometimes be 

 observed that when a long slender cloud is sailing end-long across the sky, that a 



