207 
Lussac propositam vidimus, errorem effugere studuimus 
quem miror, etiam a viris celeberrimis commissum esse. 
Ponitur enim et in hac formula, et psychrometrica quam 
Dr, Apjohn proposuit, J, sive caloricum vaporis latens, ter- 
minus constans. At vero et theoria assumit, et experientia, 
quatenus adhuc innotuit, docet, non esse caloris quantitatem 
quam durante evaporatione vapor latens reddit, quacumque 
temperatura constantem, sed quantitatem calorici, que deter- 
minato vaporis pondere continetur, quod in maximo densita- 
tis habetur.” 
Dr. Apjohn could not admit the applicability of this 
extract to himself, and in his vindication referred to the 
following passage, which occurs in his first paper on the 
Dew-point :—‘“ It must of course be admitted, that the ca- 
loric of elasticity of vapour varies with the temperature, and 
that it is represented by 1129 only at the temperature of 
50°, a point chosen by me as being nearly the mean tem- 
perature of Dublin. In strictness, the number employed 
should be 967 + 212 — #’, but it would be easy to show that 
the uniform use of 1129 cannot give rise to any material 
error.” The latter part of this passage, he observed, was 
intended only to apply to the meteorological use of his for- 
mula, and not at all to it when employed in the investigation 
of the question of gaseous specific heat. And had M. Suer- 
man repeated the calculation of his experiments he would 
have found that he, Dr. A., had, while engaged with the 
specific heats of the gases, invariably employed the rigorous 
method of estimating the caloric of elasticity of vapour. 
Dr. A. then drew attention to a tabular view of his 
results compared to those of Suerman, from which it ap- 
peared that there was a very close correspondence between 
them, a correspondence noticed and admitted by Suerman 
jn the following passage: “‘siquidem ad diversissimum atten- 
damus apparatum quo usus est, fatendum satis bene sibi con- 
venire experimenta D"* Apjohn, atque nostra. Utraque 
