12 PROFESSOR C. V. BOYS ON THE 
The Laboratory and Accessories (Plate 2). 
The apparatus is set up in the vaults under the Clarendon Laboratory at Oxford, to 
fit which, in fact, it was specially designed. I cannot sufficiently express my obligation 
to Professor Ciirron for giving up to me entirely for four years this very perfect 
observing room, for not only was I able to make my observations under speciaily 
favourable conditions, but I have had the advantage of having at hand the resources of 
his splendidly equipped laboratories, and of being allowed to make any use of them 
that. I desired. I feel that Professor Ciirron’s kindness in the matter is the greater 
as I have no claim upon him whatever, and I can only hope that in so far as my work 
carried out in his rooms may represent progress in practical physics, he may feel 
justified in haying sacrificed to this end his best observing quarters. 
The vault is a double one, of which the southern half is shown in plan im fig. 18. 
This is separated from the northern half by two piers. The entrance is by a door at 
the east end of the northern half. The two tables, A,, Aj, which Professor CLirron 
had built for the purpose of the experiment in the positions shown, are of his standard 
pattern. The top, made of one slab of slate, rests on a large block of freestone, and 
this is supported by three walls of brick set in cement, forming an H. ‘The instrument 
surrounded by the octagon house is placed upon the table A,. On the table A, is 
arranged a large astronomical telescope T, by Cooke, of York, by means of which the 
scale is read by reflection from the mirror. The great focal length and the perfection of 
the object glass are necessary to obtain sufficient magnifying power to be able to read 
with certainty to =}5 inch on the scale; the large diameter of 4 inches has the 
advantage of giving a large field of view, which is almost essential in taking rapid 
transits. Moreover, telescopes of the same perfection of construction and length are 
not immediately obtainable of smaller diameter. This telescope is supported by two 
cast-iron standards, each with its own travelling V, of my own construction, which 
give absolute steadiness, being geometrically designed. In this way a considerable 
range of height can be obtained in case it is wanted. The small telescope ¢, for 
reading the vernier V, by which the angular position of the lid and of the large balls 
M M is determined, also stands on the table A,. Besides the telescopes, a pulley- 
wheel p, rests upon the table, and a driving-wheel d is clamped to it; p, is pulled 
by a stretching weight, so as to keep the blind cord b passing round the other wheels 
P2, Ps and fastened to the go-cart g in a state of tension. The cart is a beautifully 
executed specimen of part of a “natural philosophy set” of the last century, and was 
lent me by Mr.G.S. Newrs. It runs on the wooden framework, which is wedged into 
the recess at the east end of the room, between a pair of rails made of angle brass. It 
carries an albo-carbon lamp, so that the flame can be brought behind any division of 
the great scale 8, which may be seen in the telescope T by reflection from the mirror. 
The flame is turned down very low to avoid heating the room unnecessarily. I 
