AT KEW OBSERVATORY AND THEIR DISCUSSION. 493 



and with one or two exceptions e.g., a paper by Mr. L. AUSTIN, in ' Wied. Ann.,' 

 vol. 50, 1893 the theories they dealt with seemed of a hopelessly involved character 

 for practical application. I did indeed try one or two" of the formula? proposed, but 

 conditions so complicated as those of the Kew aneroid test soon led to expressions 

 of a formidable character. The numerical results I actually reached did not show 

 a promising accord with experiment, and having regard to the many claims on my 

 time, 1 did not push the calculations further. 



8 48. The following are the only earlier investigations on aneroid barometers, 

 having any direct bearing on the results of the present paper, that have come under 

 my notice : 



1. "On the Errors of Aneroids at Various Pressures" (Dr. BALFOUR 

 STEWABT), ' B.A. Keport,' 1867, pp. 26, 27, of 'Transactions of the Sections.' 



2. " An Account of Certain Experiments on Aneroid Barometers made at 

 the Kew Observatory at the Expense of the Meteorological Committee " (Dr. 

 BALFOUR STEWART), ' Hoy. Soc. Proc.,' vol. 16, 1869, pp. 472-480; 'Phil. 

 Mag.,' vol. 37, 1869, pp. 65-74. 



3. " How to Use the Aneroid Barometer," by EDWARD WHYMPER ; 

 London : JOHN MURRAY, 1891. 



Of these, No. 1 is a preliminary report apparently of the work more fully dealt 

 with in No. 2. It mentions the tendency in the reading to fall under continued 

 exposure to low pressure, and also the general nature of the recovery after return to 

 atmospheric pressure. 



No. 2 commences with a slight reference to the secular variation of zero. It then 

 describes some tests showing that at atmospheric pressure changes of temperature 

 have little effect on "well-made compensated" instruments. The writer adds, "I 

 am unable to say what effect a change of temperature would have at a diminished 

 pressure." 



The main part of the paper describes the phenomena observed in pressure cycles, 

 30-19-30 inches of the following kind. Pressure was reduced an inch and then 

 kept steady for 10 minutes, when a reading was taken; it was then lowered a 

 second inch, and so on. At the lowest pressure there was a stoppage of l hours, and 

 thereafter pressure was raised at the same rate as it had been lowered. The 

 aneroids were always tapped before reading. The general superiority of large to 

 small aneroids, and the increase in the tendency to creep when the range is lengthened 

 are duly noted. The effects of stoppage on the top of a mountain are also 

 remarked on. 



A considerable number of aneroids were examined. The object was apparently, 

 however, rather to ascertain the conditions under which they behaved fairly con- 

 sistently than to investigate whether the variation in the readings obeyed any 

 ascertainable laws. 



