AT KEW OBSERVATORY AND THEIR DISCUSSION. . 499 



hands similar certificates come that the corrections stated in them are good under 

 all conditions and for all time." In view of the footnote to the certificate, calling 

 attention to the probable recovery from the residual error, exhibited on return to 

 the original pressure, this standpoint could hardly, T think, be justified ; and judging 

 by a footnote to his p. 52 Mr. WHYMPEB would presumably allow this himself. At 

 the same time, he apparently considers it a point of view likely to present itself to 

 travellers, a class as to whose scientific knowledge and general intelligence he is 

 better qualified to speak than I am. If he is right in his conclusion, a change in the 

 certificate is certainly desirable. 



Before concluding my reference to Mr. WHYMPER'S interesting pamphlet, I would 

 take the opportunity of explaining that the rate of change of pressure in the 

 ordinary Kew test is not, as he states on several occasions, about t inch in 2 minutes ; 

 the actual rate is only about half this. 



55. The 75 special experiments some of a very tedious and exacting character 

 on which this paper is mainly based, were carried out with great care and discretion 

 by Mr. W. HUGO, Senior Assistant at Kew Observatory. In addition to the obser- 

 vational work, Mr. HUGO reduced all the barometer readings and carried out some 

 of the subsequent arithmetical operations. The bulk of these and the checking of 

 the reductions were undertaken by myself. 



It is, I allow, anomalous, and from various points of view undesirable, that a 

 scientific man should have himself performed none of the experiments which he 

 discusses. When, however, as in the present case, observation is being pushed 

 to the utmost capabilities of the instruments employed, the absence of preconceived 

 ideas in the actual observer is a valuable compensation. 



3 s 2 



