5 
1909-10.] Andrews’ Measurements of Compression. 
Having by means of this expression calculated the pressure corre- 
sponding to a given volume v of hydrogen at temperature T( = £° C. + 273) 
we obtain the pressure to which the mixture was subjected by applying 
the small correction for the difference of levels of the mercury in 
the two tubes. The true pressure so calculated is entered in the sixth 
column of the third set of tables. It will be found that these are all 
somewhat higher than the values given by Andrews in the posthumous 
paper of 1887 {Phil. Trans., vol. 178, pp. 45-56; Scientific Papers, 
pp. 457-471). 
There are three sets or groups of tables corresponding to the memoirs 
already mentioned, the first and second Bakerian Lectures of 1869 and 
1876, and the posthumous paper of 1887. These are distinguished as 
Groups A, B, and C. 
In following out Professor Tait’s desire to have the data of Andrews’ 
classical experiments in as accurate a form as possible, I do not think 
that any apology is needed. Professor Andrews was a born experimenter 
who spared no pains to secure absolute accuracy in all his work. The 
data are now presented in such a form that the pressures can be deter- 
mined with accuracy. They must of course be studied in connection with 
Dr Andrews’ own original descriptions as contained in the three important 
memoirs of 1869, 1876, and 1886. 
Lengths are in millimetres, volumes in cubic centimetres, temperatures 
in degrees centigrade. 
A positive sign after the Difference of Level in the last column means 
that the level in the manometer tube was the higher, so that, in order to 
find the pressure of the carbon dioxide, the corresponding pressure must 
be added to the pressure as indicated by the manometer; on the other 
hand, a negative sign means that the correction must be subtracted. 
