207 



Lussac propositam vidimus, errorem effugere studuimus 

 quern miror, etiam a viris celeberrimis commissum esse. 

 Ponitur enim et in hac formula, et psychrometrica quam 

 Dr. Apjohn proposuit, /, 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, quae 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 Dubhn. In strictness, the number employed 

 should be 967 -f- 212 — t\ but it would be easy to show that 

 the uniform use of 11 S9 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 

 in the following passage : " siquidem ad diversissimum atten- 

 damus apparatum quo usus est, fatendum satis bene sibi con- 

 venire experimenta D"^* Apjohn, atque nostra. Utraque 



