96 Mr. J. T. Bottomley on Expansion with Rise of 



but not to the same extent ; and neither came back to its 

 original length. This was of course to be expected. But 

 it turned out, on repeating the heating and cooling, that the 

 same thing occurred again and again ; and it was not till 

 after about 150 heatings and coolings that the heavily loaded 

 wire assumed a permanent state, expanding and contracting 

 by equal amounts with the heating and cooling *. The lightly 

 loaded wire took its permanent condition much sooner. 

 This itself was a valuable result, applying directly to the early 

 observations on the secular wires in the University tower. 



Fig. 1, PI. IX., shows the arrangement for these preliminary 

 experiments. Behind the wire a half-millimetre scale was put 

 up; and each wire carried a pointer moving over the scale. The 

 readings at hot and cold temperatures were taken with the well- 

 known Quincke microscope-kathetometer ; and the process and 

 observations were carried on, as has been said, till each 

 pointer gave unvarying readings at the hot and cold tempe- 

 ratures. It was then considered that the wires had assumed 

 a permanent condition. 



The pointers and scale were now removed and two hooks, 

 of peculiar construction, figs. 2 and 3, were attached to the 

 ends of the wire, the wires being passed into holes made for 

 the purpose and soldered in. These hooks carried and formed 

 part of the stretching weights. The upper parts of the hooks 

 are turned over to form two horizontal plates, and the vertical 

 parts ' of the hooks press very lightly against each other and 

 form almost frictionless guides one for the other. In one of 

 the vertical faces a vertical V-groove is cut, while the 

 remainder of the face is plane and well-polished. Two little 

 feet on the vertical face of the other hook move in the 

 V-groove of the first, and a third foot rests against the smooth 

 vertical face. A relative geometrical guide is thus provided 

 for the hooks, and the shape of the hooks is such that the 

 gravity of the whole, including the weights, gives the requisite 

 slight pressure of the one against the other. The horizontal 

 parts of the hooks just mentioned carry what is practically 

 a small three-legged table, of which two legs rest on one 

 platform and the third on the other. To be more precise, one 

 of the platforms carries on its top a little plate with a 

 V-groove cut in it ; and a knife-edge, cut away at the central 

 parts and thus leaving two feet at the extremities, attached 



* I must not fail to express here my indebtedness to Mr. Thomas A. B. 

 Carver, assistant, and Mr. W. S. Cook, student in the Physical Laboratory, 

 who carried out these experiments in the winter sessions 1887-8 and 

 1888-9 respectively. Without their patient labour the work would have 

 been impossible to me. 



