118 Rev. W. V. Harcourt on Lord Brougham's statements 



discovery of the difference of specific gravity in several gases, 

 by Cavendish. 



You do not distribute their honours to any of these great 

 discoverers with a severe attention to matter of fact ; but I 

 must do you the justice to own that you preserve a principle 

 of equity in your adjudications. You omit, it is true, to dwell 

 upon, or even to mention, the main point of novelty in the re- 

 searches of Black ; but then you give to Black the discoveries 

 of Boyle and Cavendish, and make it up to Cavendish by allow- 

 ing him a slice of the merit which belongs to Galileo. 



For Cavendish you say, " He carried his mathematical 

 habits into the laboratory; and not satisfied with showing the 

 other qualities which make it clear that these two aeriform sub- 

 stances are each sui generis, and the same from whatever sub- 

 stances, by whatever processes they are obtained, — not satis- 

 fied with the mere fact that one of them is heavier, and the 

 other much lighter than atmospheric air," (a previous ac- 

 quaintance with all which facts you have taken care to ascribe 

 to Dr. Black) " he inquired into the precise numerical relation 

 of their specific gravities with one another and with common 

 air, and Jirsl showed an example of weighing permanently elastic 

 Jluids : unless indeed Torricelli may be said before him to have 

 shown the relative weight of a column of air and a column of 

 mercury, or the common pump to have long ago compared in 

 this respect air with water. It is however sufficiently clear 

 that neither of these experiments gave the relative measure of 

 one air with another; nor indeed could they be said to com- 

 pare common air with either mercury or water, although they 

 certainly showed the relative specific gravity of the two bodies, 

 taking air for the middle term or common measure of their 

 weights." 



What a strange qualification of a still stranger assertion ! 

 If instead of this confusion of specific gravities with equipon- 

 derant columns, ending with the grave suggestion, that " the 

 relative specific gravities of water and mercury " might have 

 been taken by the intermediation of " air," you had said that 

 philosophers have attempted, from the relative heights of the 

 barometer at different elevations, to calculate the mean spe- 

 cific gravity of the atmosphere*, there would have been mean- 



* The following quotation will show the nature of these calculations 

 (Dan. Bernoulli Joh. Fil. Hydrodynainica, ilrgcntorati, 1738. Sect. 10. 16. 

 p. 209) : — " Patet exinde quid censendum sit de ilia methodo qua in Anglia 

 aliquando usos esse recenset D. Du Hamel, in Hist. Acad. Sc. Paris, ad 

 indagandam rationem inter gravitates specificas aeris et mercurii : ob- 

 servata nimirum altitudine mercurii in loco humiliori, turn etiam in altiori, 

 gravitates specificas in aere et mercurio statuerunt, ut erat differentia 



