130 
In the tables annexed table I gives the mean monthly 
readings of the thermometers for each year, with the addi- 
tional readings of the black bulb freely exposed, and also 
that of the maximum thermometer in the shade. 
Looking at the yearly means, the black bulb in vacuo 
gives the highest mean reading, the one with carbonic acid 
gas comes next, followed by the condensed air one, that 
filled with hydrogen giving the lowest temperature. 
Examination of the monthly values shows that the maxi- 
mum for all the thermometers occurs in July, and the 
minimum in January. The minima of the enclosed ther- 
mometers read nearly all alike ; with the maxima the vacuo 
and carbonic acid ones are nearly equal, and the same remark 
applies to the hydrogen one and the one filled with com- 
pressed air ; the latter agrees with what Tyndal points out, 
that hydrogen and atmospheric air absorb heat equally. 
Table 3 gives the differences of each monthly mean 
referred to the reading of a freely exposed black bulb 
thermometer. 
In volume 5, page 169, of Symons’s “ Meteorological 
Magazine,” there is a paper by Mr. Francis Nunes, giving 
comparisons of carefully made black bulb thermometers by 
Pastorelli, showing a considerable difference between the 
thermometer in vacuo and the one partially exhausted; his 
observations were made in October, and show a difference of 
l - 2° to 1T5, the vacuo thermometer being the highest of the 
two. Mr. Nunes also states that an enclosed thermometer 
without any exhaustion reads still lower, being from 08° to 
12 - 8 below the vacuum thermometer. 
From my observations the difference between the vacuo 
and condensed air thermometers is never very large, 
amounting rarely in individual cases to 5 0 to 60°, but in 
July, 1865, reached occasionally 10 - 0 J : the mean difference 
in July only reaching 4 -3°. 
I am not aware of any similar series of observations to be 
found anywhere else, and thought it might be desirable to 
tabulate the values for comparison with any subsequent 
series that may be made. 
