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.'

The following Preliminary Report on my work on board the 'Challenger’ during the last three years has been drawn up in compliance with a request on the part of Professor Wyville Thomson, which was communicated 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.