( 88 ) 
before) if the barometer-readings had been reduced to one tempe- 
rature, in other words, what are the values of the true temperature- 
coefficients. For 760 m.m. the reduction for 1° Réaumur amounts to 
0,152 m.m., of which the effect on the rate is 0'.0021. Consequently 
the 4e temperature-coefficient is found by applying a correction of 
+ 00021 to the apparent value. 
7. We shall now apply to the reduced mean rates the reductions 
due tothe corrections found for the temperature-coefficient. The adopted 
corrections are of this coefficient: 
1878 May—1884 April 6¢=>-+ 39 
1884 May—1893 April 0 
1893 May—1898 July +75 
Though probably the values mentioned at the end of § 6 are 
preferable, it did not seem necessary to repeat the computations with 
these altered values. 
After this the deviations of the corrected monthly means from the 
values of a) derived from the curve were formed and these 
means were arranged in yearly groups, each year beginning with 
May. ®) For brevity’s sake L do not give the results for the separate 
years, but only the means for four groups of years, viz: 1879—1882, 
1883—1886, 1887 —1891 and 1892—1896. If the deviations of the 
monthly means from the yearly means are used, the mean results 
for those four groups are not appreciably altered. All values are 
given in units of one thousandth part of a second. 
It will be seen that the results of the first and the second groups 
agree very well inter se, and also those of the third and the fourth 
groups, I have therefore finally formed the means for the periods 
1879—1886 and 1887—1896. The principal difference between these 
two periods seems to be that the low minimum in October which 
is shown in the first, has disappeared in the last. In the years, 
1892—1896, however, the whole periodicity begins to be less marked, 
and in 1897 it is no longer shown by the monthly means. The 
monthly means of 1878 (i. e. ’78 May—’79 April) are in good 
agreement with the results for the period 1879—1886. 
1) Since this curve is relative to the temperature + 10°, while the mean yearly 
temperature is + 8°.7 its first and last part had to be slightly altered, to account 
for the altered values of the temperature-coefficient. 
2) The curve for a can only be drawn from 78 Noy. to “98 Jan., therefore 
the present investigation can only include the period "79 May—’97 April. 
