AT KEW OBSERVATORY AND THEIR DISCUSSION. 



449 



Two aneroids, No. 1 and No. 4, were subjected to all these experiments ; two 

 others, No. 2 and No. 3, divided only to 20 inches, were not taken below 21 inches 

 of pressure. 



The order of the experiments was adopted with a view to the possible permanent 

 influence of the lower pressures on the aneroids. 



The procedure in these experiments was uniform. The change of pressure during 

 both the descent and the ascent was at the rate of 1 inch in 5 minutes. At the 

 lowest point there was a stoppage of 10 minutes, preceded however by no slight 

 lowering of pressure below the point at which the last descending reading was taken. 



After each experiment the aneroids were left for some days at atmospheric 

 pressure, so as to be fully rested at the beginning of each pressure cycle. The 

 experiments were made in 1895, and extended over a period of five mouths. As will 

 be seen later, there would not appear to have been any serious change in the after- 

 effect phenomena during this interval. 



8 The first thing investigated was the law of variation throughout each range of 

 the differences of the descending and ascending readings, it being advisable to make 

 sure that the aneroids were fair specimens, and gave results sufficiently similar in 

 type to those derived from the old verification books. I have thought it unnecessary 

 to reproduce the results analogous to Table I., but pass at once to those analogous to 

 Table II. The procedure followed was exactly the same as that already described, so 

 that the results of Tables III. and II. are immediately comparable. 



TABLE III. (Special Experiments). Ratios of Differences Descending less 

 Ascending Readings to Mean Difference. 



The alteration required to make the sum of the ratios in the last line exactly 11, was 

 slightly greater than in the case of Table II., but still was less than one half per cent. 



There is a tendency in the values at the extremities of all the ranges to be lower 

 in Table III. than in Table II., entailing of course a slight difference in the opposite 

 direction towards the centre of the range. This is probably due mainly to the 

 difference between the procedure followed in the old and new observations, The 



VOL. cxci. A. 3 M 



