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i REPORT — 1902. 



set up in the same manner, but from materials supplied by various makers, 

 and these have been traced to the mercurous sulphate. The observers at 

 the Reiclisanstalt have come to a similar conclusion.' Dr. Carpenter and 

 Mr. Smith are now engaged in experiments at the National Physical 

 Laboratory, the results of which, it is hoped, will enable them to specify 

 a method of preparing mercurous sulphate which will lead to consistent 

 results for the E.M.F. of the cells. 



The air- condensers belonging to the Committee have been set up, and 

 a number of determinations of their capacity have been made by ]\Ir. 

 Campbell. The results of these, though at present they are only to be 

 treated as provisional, show that the condensers are in good ordei", and 

 have suffered no damage by their journeys Krst to Liverpool and then to 

 Richmond. The capacity of one is nearly the same as when at Cam- 

 bridge ; that of the other has altered very slightly. With a view of 

 establishing a standard of capacity a number of other comparisons between 

 the standards of the Association and those of Dr. Muirhead are in 

 progress. 



In this comparison work some difficulty has arisen from the fact that 

 all the i-esistance-boxes belonging to the Association are of platinum- 

 silver. The small temperature coefficient of manganin gives that material 

 a very distinct advantage, and the Secretary has been endeavouring to 

 use it whenever possible. It would be of great service for this part of the 

 work to have a subdivided megohm-box in manganin, and the Committee 

 trust that funds for this may be forthcoming. They hope in their next 

 report to give a detailed account of the condenser experiments. 



The construction of platinum thermometers as standards for high 

 temperature thermometry has made some progress. The National Phy- 

 .sical Laboratory was not opened until March, and the work of .setting up 

 the apparatus, carrying out the necessary calibrations, &c., has occupied 

 most of the time of the assistants since then. 



After some further experiments however, to test the purity of the wire 

 it was proposed to u.se had been carried out, a stock of eight ounces of wire 

 of the highest purity and of a thickness varying from six to eight 

 mils has been bought from Messrs. Johnson & Matthey, while four 

 ounces of the same wire, but of twenty-two mils in thickness, suitable 

 for leads or for drawing down to special sizes, have also been secured ; and 

 six thermometers are in course of construction in the workshops of the 

 Laboratory under Dr. Harker's supervision. 



Of these six thermometers two of live ohms fundamental interval will 

 be hermetically sealed in glass tubes, and will serve as standards for low- 

 temperature work ; a second pair, having an interval of one ohm, in tubes 

 of hard glass — probably Jena — 59'" — will serve for temperatures up to 

 050° C, while the third pair, also of one ohm interval, in porcelain 

 6ubes, will be employed up to 1100° or 1200° C. It is hoped by the use 

 of quartz to extend the range of temperature considerably, and some ex- 

 periments are in progress with this object. 



Two electrical resistance ovens have been built by Dr. Harker for 

 high-temperature work, and these serve their purpose admirably. 



The grants voted during the past two years have been expended on 

 the purchase of the materials for the platinum thermometers, and addi- 

 tional sums are necessary to complete their manufacture. 



' T/idtigJieit dcr riiys.-Tcch.-Itcichsanstalt, 1001-1902. 



