I 



November 14, 1895] 



NATURE 



43 



^Fig. 3), then the outer framework ABA' moves instead of the 

 inner block. 



The arrangement by which the pads in the block H can be 

 either pressed down for temporary, or screwed down for more 

 permanent, observations is shown by the section in Fig. 3. 

 The spring M N lifts the pads off the bridge and galvanometer 

 wires, which therefore do not touch the cross-wire (whose section 

 is shown at W) unless a downward pressure is exerted on the 

 })lock H. 



By holding the head of the screw S the whole contact-maker 

 can be pushed to any desired position. 



The vernier is shown at F H (Fig. 2). 



The box contains coils of 20 and 100 ohms, which can be 

 thrown into the battery circuit by means of a switch, and also 

 a galvanometer shunt of about ^V <^he galvanometer resistance. 



With the exception of the points to which I have drawn 

 attention, the resistance-box resembles those ordinarily in use. 



The galvanometer has a resistance about 5 ohms, and is 

 sensitive and " dead-beat." A fixed scale is placed before the 

 mirror, and the image viewed through a microscope. Very 

 small deflections can thus be observed, and observations can be 

 taken in bright daylight. 



This last has a coil whose resistance is 2 '5 times as great as 

 he preceding ones. 



All these thermometers have been annealed at a temperature 

 of about 1000" C, Nos. 5 and 6 being temporarily placed in 

 porcelain tubes for that purpose. 



The apparatus for the standardisation in ice, steam, and sulphur- 

 vapour presents certain distinctive features, most of which, how- 

 ever, are described in Phil. Trans. Koy. Soc, vol. 182 A. 



Messrs. Heycock and Neville were so kind as to undertake 

 the design and arrangement of the furnaces, &c., for the high 

 temperature work, which are, in the main, similar to those used 

 during this summer for the purposes of their investigations into 

 the behaviour of alloys. As an account of their work will 

 shortly be published, I shall not venture to anticipate it by any 

 description. Arrangements have been made for (i) the 

 standardisation of thermometers by observations on the freezing- 

 point of silver when placed in a reducing atmosphere ; ^ (2) the 

 comparison of the Kew standards with other thermometers over 

 the range icxd° to 300° C. by means of a well-stirred bath of a 

 fusible metal covered with paraffin or oil ; (3) the comparison 

 over a range 300° to 1200° C. in a bath of melted tin placed in a 

 reducing atmosphere. 



Thermo-electric effects (which at high temperatures are 

 •occasionally considerable) are eliminated by the use of a special 

 key described in Phil. Trans. Roy. Soc, vol. 184 A, p. 397, 



The leads from the box to the thermometer are about five 

 yards in length, and are each composed of 136 strands of copper 

 wire carefully insulated. The thermometers can thus be used 

 in any part of the room. 



Six thermometers have been supplied, all of whose coils are 

 formed from the same sample of specially pure platinum wire — 

 tliameter 0"C)o6 inches. The length of wire in Nos. i to 5 is 

 about 18 inches, the mica framework which supports the coil is 

 from i\ to I J inches in length, and this portion is termed the 

 bulb. 



Nos. I and 2 are contained in porcelain tubes i "2 cm. in 

 diameter, 40 cm. long. 



Nos. 3 and 4 are contained in porcelain tubes i'5c.m. in 

 diameter, 36 cm. long. 



No. 5 is contained in a glass tube l "4 cm. in diameter, 40 cm. 

 long. 



No. 6 is contained in a glass tube I 7 cm. in diameter, 40 cm. 

 long. 



NO. 1359, VOL. 53] 



The whole of the apparatus is placed in a special building 

 erected for this purpose by the Kew Committee, according to 

 designs by Mr. W. N. Shaw, F.R.S., and myself, after 

 consultation with Messrs. Heycock and Neville. The building 

 is found to admirably fulfil its purpose, the only drawback 

 being the defective gas supply, which will, however, shortly be 

 remedied by the insertion of a larger main between the 

 Observatory and the outbuildings. 



Fig. 4 (a copy of a photograph by Mr. Hugo) gives the rela- 

 tive positions of box and galvanometer. It will be seen that 

 the observer can manipulate the contact-maker without removing 

 his eye from the galvanometer-microscope, a great advantage 

 when observing small temperature changes. Immediately to the 

 right of the resistance box, but exterior to the limits of this plate, 

 is a large draught-chamber containing the furnaces, &c. 



III. The Standardisation of the Apparatus. 

 The necessary operations were as follows : — 

 No. I. Determination of the temperature coefficient of coils 

 and bridge-wire. 



1 See letter to Nature, October 17, 1895. 



