70 



Mr. E. H. Scott. 



series of observations at Washington, he handed them over to th. 

 officers of the United States Coast Department. Snbseqnently Professor 

 C. S. Peirce, of the United States Coast Survey, who had made a series 

 of pendulum observations at Kew and elsewhere in 1876, visited the 

 Observatory in July, 1883, and made a subsidiary series of experiments 

 with a view of determining the flexure of his stand when on the Kew 

 piers. 



1882. In April of this year the Chairman announced the comple- 

 tion of the long series of reductions of the Kew Photoheliograph 

 measurements, extending over the period February 7th, 1862, to April 

 9th, 1872. He stated that the MSS. volumes containing the results 

 had been deposited for reference with the Royal Society, and that the 

 w r hole of the sun-pictures had been re-measured at the Observatory, 

 and reduced by Mr. A. Marth, F.R.A.S., so as to give the heliocentric 

 longitudes and latitudes of the spots, as well as their areas. 



The entire expense attendant on these reductions, which has 

 amounted to the considerable sum of 1,452Z. 6s. 7d., was defrayed by 

 Mr. de la Rue. This amount was in addition to the sums that gentle- 

 man had previously disbursed in contributing to the maintenance of 

 the Photoheliograph, and the prosecution of solar research. The total 

 amount of his payments towards this branch of the Observatory work 

 has reached the large sum of 2,071 1. 15s. 4c?. 



In the same year the Committee received very gratifying testimony as 

 to the accuracy of the Standard Thermometers constructed at the Obser- 

 vatory. In a paper contributed to the "American Journal of Science," 

 Dr. Leonard Waldo, of the Winchester Observatory, Tale College, 

 U.S.A., remarks that after a critical examination of three Kew Standard 

 Thermometers, in which every degree was separately measured, entail- 

 ing no less than 2,300 micrometer readings, he came to the conclusion 

 that their errors are practically insensible, and too small to be detected 

 with certainty. 



Professors Thorpe and Riicker also tested very minutely three similar 

 instruments made for them at Kew. In a paper read at York before 

 the British Association, Professor Riicker stated, "In no case would 

 the calibration error in the determination of a difference of tempera- 

 ture have amounted to 0*02° C. It may therefore be concluded that 

 Welsh's method, as applied at Kew to selected tubes, and with a 

 measuring instrument of great accuracy, is capable of giving first-rate 

 results. The errors which remain when it has been applied are so 

 small that they may be neglected in all cases but those where the 

 thermometers are to be used under the most favourable conditions, 

 i.e., with the stem of the same temperature as the bulb, &c. This 

 satisfactory conclusion is confirmed by the fact that Professor Rowland 

 has recently stated that the calibration of the Kew thermometer used 

 by him in his research on the mechanical equivalent of heat was 

 practically perfect." (British Association Report, 1881, p. 541.) 



