Page:Popular Science Monthly Volume 10.djvu/732

712 and which, though it has been in constant daily use for more than twenty years, is as true and serviceable as ever.

If at any time the geologist has occasion to lighten his equipment for some long mountain-expedition, where every additional ounce of weight begins to tell by the end of the day, and where, therefore, for the sake of doing as much and holding out as long as possible, he should carry nothing that is not absolutely needful for his purpose, he may advantageously combine the pocket-compass and clinometer in the one instrument to which I have already alluded. This convenient instrument is about the size of an ordinary gold watch. It consists of a thin, round, flat, metal case, shaped like that of a watch, and covered either with a common watch-glass, or, still better, with a flat disk of strong glass. Instead of figures for the hours and minutes, the white enameled face of this geological watch is that of a common pocket-compass. But the interval between each of the four cardinal points is divided into 90°. On the central pivot, just underneath the needle, a small brass pendulum is placed, and a straightedge of metal is soldered on one side of the outer rim of the watchcase in such a position that the instrument will stand on it if need be, and the pendulum will then point to zero. A simple piece of mechanism passing through the handle enables the observer to throw the needle off the pivot, or let it down, as he may require.

As it is impossible for a field-geologist to remember the details of all the observations he makes on the ground, or to insert them on a map, he regards a good note-book as an essential part of his apparatus. From the nature of his work, he has frequently occasion to make rough sections, or diagrams, and, if possessed of the power of sketching, he has abundant opportunity of aiding the progress of his researches by jotting down the outlines of some cliff, mountain, or landscape. Hence, his note-book should not be a mere pocket memorandum-book. A convenient size, uniting the uses of a common note-book and a sketch-book, is seven inches long by four and a quarter inches broad. Let me remark, in passing, that perhaps no accomplishment will be found so useful by the field-geologist as a power of rapid and effective sketching from Nature. If he has this power in any degree, he ought sedulously to cultivate it. Even though he may never produce a picture, he can catch and store up in his note-book impressions and outlines which no mere descriptions could recall, and which may be of the highest value in his subsequent field-work. This is true of ordinary detailed surveys, and still more of rapid reconnaissances, which may have their ultimate usefulness enormously increased if the observer can seize with his pencil and carry away the forms of surface as well as the geological relations of the region through which his traverse lies.

As every device which saves labor and time in the field, or which adds to the clearness of the work, is deserving of attention, I would