On Work done on board H.M.S. c Challenger J 593 



VI, " Preliminary Report to Professor Wyville Thomson, F.R.S., 

 Director of the Civilian Scientific Staff, on Work (Chemical 

 and Geological) done on board H.M.S. ' Challenger/ By 

 J. Y. Buchanan, Chemist and Physicist to the Expedition. 

 Communicated by Professor Wyvtlle Thomson, E.R.S. Re- 

 ceived March 7, 1876. Read March 16. 



The following Preliminary Report on my work on board the ' Challen- 

 ger ' during the last three years has been drawn up in compliance with 

 a request on the part of Professor Wyville Thomson, which was com- 

 municated to me on the 23rd June, 1875. As my time at sea is fully 

 occupied with the daily laboratory work, I was obliged to postpone 

 preparation of the report until our arrival at Valparaiso, where the 

 whole of my time was devoted to it. Three weeks, however, is too short 

 a time to prepare even a preliminary report with satisfaction, and there 

 are doubtless many things in the present one for which I must crave 

 indulgence. In venturing to publish the few geological notes which I 

 have embodied, I feel that a special apology is required, as my knowledge 

 of rocks is, at best, but superficial. I was emboldened to do so, however, 

 by considering that the islands to which the notes refer are principally 

 such as are but seldom visited by any one, and that, as it was my good 

 fortune to be able to visit them, it was right that I should make what 

 observations I could and record them, in case amongst them there might 

 be some which would be of value to the geologist. 



Observations on the Specific Gravity of Sea-water* 

 As the value of these results depends to a great extent on the nature 

 of the means taken to collect the water, and on the delicacy of the 

 instrument used for determining its specific gravity, I shall shortly 

 describe them both. 



The samples of water are collected either in an ordinary canvas 

 bucket, or in one of two kinds of metal "water-bottle," according as it 

 is to be taken from the surface or from depths below it. The use of the 

 ordinary hand-bucket needs no explanation. When water is to be 

 obtained from the bottom, the " slip " water-bottle is used. This instru- 

 ment is a Swedish invention, improved by Dr. Meyer, of Kiel, who with- 

 out doubt has described it, and by Messrs. Milne, of Edinburgh, who 

 furnished those on board the ' Challenger.' 



Water from intermediate depths is obtained in a much lighter instru- 

 ment, which, with a drawing and the method of usiug it, is fully 

 described in a paper presented to the Royal Society in the early part 

 of 1875, of which an abstract has been published in the ' Proceedings/ 

 ]S T o. 160. It consists of a metal cylinder furnished with stopcocks at 

 both ends. The levers by which these stopcocks are turned are con- 



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