1879.] Results of Magnetical Observations, 1875-76. 



29 



solid, a salt of the same kind is the nucleus, and that such a nnclens is 

 present in the air, I must leave the proof of the assertion to those who 

 make it or defend it. I cannot imagine what can be the sonrce of the 

 alum nucleus, for example, in the above experiments, limited as they 

 were by such well-defined conditions. M. Gernez can only account 

 for the existence of alum in the air on the supposition that as a good 

 deal of that salt is used in dye-works, it must escape into the air from 

 such a source. Until it can be proved that on a wet day and while 

 rain is still falling there is alum in the open air, I must continue to 

 maintain my original statement that alcohol is, under proper condi- 

 tions, capable of determining the solidification of these solutions. 



I have several times noticed the persistence of nuclear action on the 

 part of a dense charcoal, such as that made from box-wood. A small 

 piece of such charcoal was boiled in a solution of potash alum (1 to 3). 

 When cold, a large crystalline mass was found attached to the char- 

 coal. The flask was reboiled five times in the course of a week, and 

 each time the same result appeared when the flask had become cold. 



I have referred to bread as a nucleus, and the action is curious. 

 New bread is not nuclear ; but if stale bread, such as a second day's 

 loaf, be cut open with a clean knife, and bits of the crumb be dug out, 

 they act powerfully as nuclei on solutions of sodic sulphate and alum. 

 If such bread be slowly toasted before the fire, it becomes inactive ; 

 but if it contain alum, it is active on solutions of potash or ammonia 

 alum (about 1 to 1), whether the bread be new or stale, toasted or 

 not. Treated by this test, I have found the bread of Highgate to 

 contain alum ; but some bread from Drury Lane gave most decided 

 evidence of its presence. 



III. " On the Results of the Magnetical Observations made by 

 the Officers of the Arctic Expedition, 1875-76." By Staff- 

 Commancler E. W. Ceeak, R.N., attached to the Admiralty 

 Compass Department. Communicated by Captain F. J. 0. 

 EVANS, C.B., F.R.S., Hyclrographer of the Admiralty. Re- 

 ceived April 25, 1879. 



The following narrative and results form the sequel to the " Memo- 

 randum on Terrestrial Magnetism," prepared by Professor J. C. 

 Adams, M.A., F.R.S., and Captain F. J. Evans, R.X., F.R.S., pub- 

 lished in the " Manual and Instructions for the Arctic Expedition, 

 1875," suggested by the Arctic Committee of the Royal Society. 



The " Alert " and " Discovery " left Portsmouth on the 29th May, 

 1875, and on arrival at Godhavn, in Disko, the first magnetic obser- 

 vations were made. The values of the declination and inclination 



