104 BEPOET — 1878. 



wires above the gun-metal plate, or of attaching the weights to their 

 lower ends. No thoroughly satisfactory mode of attachment has yet 

 been found. In the course of experiments which have been carried on 

 at Glasgow on the breaking weight, and the Young's modulus of elasticity 

 of the gold, platinum, and palladium wires, which it is intended shall be 

 first suspended for examination, several modes of suspension have been 

 tried ; but it has not been found possible to make sure of avoiding very 

 considerable weakening of the wire at the points of attachment at the ends. 



At the bottom of the iron tube there is a window of plate glass 

 through which the lower parts of the wires can be viewed, and the 

 window can be drawn up so as to allow of the lower parts of the wires 

 being reached. 



In front of the window a strong gun-metal table is set up. It is sup- 

 ported, independently of the iron tube and of the floor of the room, on 

 iron brackets fixed to the stone wall of the chamber, and is very carefully 

 levelled. On this table a cathetometer is carried, by means of which 

 marks on the wires are to be observed. The cathetometer moves on the 

 table parallel to the planes of the rows of wires. It has the two back 

 feet of the triangular sole-plate on which it is supported movable in a 

 V-groove cut in the table, the third foot resting on the plane upper sur- 

 face. There is also a slot cut in the table through which a screw passes 

 up from below to the sole-plate of the cathetometer, and by means of this 

 screw the cathetometer can be clamped in any required place. 



The cathetometer is a small instrument which has been constructed 

 by Mr. James White, of Glasgow, for the purpose of these experiments. 

 The main pillar is 1 foot high. It is supported on a 3ole-plate having 

 three levelling screws. The telescope or microscope, having cross fibres, 

 is raised or lowered on this pillar on a proper geometrical slide, and has 

 also a lifting screw in connection with a vernier for giving fine adjust- 

 ment. The vertical pillar is carefully graduated ; and by means of this 

 scale the differences of levels of proper marks put upon the wires are 

 to be determined. 



The arrangements have only been completed within the last few days. 

 They require to be carefully tested in several points, and particularly the 

 cathetometer requires careful examination. There is every reason, how- 

 ever, to expect that the work will turn out quite satisfactory. As soon 

 as possible the work of testing will be completed and wires suspended, 

 measured, and marked. 



During the past year experiments in connection with this investiga- 

 tion have been carried on in the laboratory of the University of Glasgow, 

 on the breaking-weights and elastic properties of various wires. In the 

 first place the breaking-weights and the Young's modulus, or modulus of 

 elasticity for longitudinal pull, have been determined for the gold, pla- 

 tinum, and palladium wires, with which it is proposed that the secular 

 experiments on elasticity shall commence. A large number of experi- 

 ments on the effect of stress, maintained for a considerable time, in alter- 

 ing the breaking weight and the extension under increased stress of 

 various wires, have been carried on. Soft iron wire, steel wire, and tin 

 wire in particular, have been experimented upon, and already some inte- 

 resting results have been obtained, showing that prolonged application of 

 stress certainly produces a noticeable effect. 



