Remarks on Self Registering Thermometers. i 59 



a sound eye by looking at a white object with a blue glass ap- 

 plied to one eye, and a yellow glass to the other. 



The subject is obviously one attended with great difficulty, 

 and requires much more investigation than it has yet received. 



The author of the description of Mr 's vision regards 



this defect of particular eyes as presenting a formidable objec- 

 tion to the inference deduced from Mr Herschel and Dr 

 Brewster"'s experiments, relative to the overlapping of the co- 

 loured spaces in the spectrum. We cannot at all understand 

 what the objection is which is here alluded to ; nor can we con- 

 ceive how any inference from an obscure physiological fact 

 could set aside the result of a legitimate induction. 



Art. XXVI,— r- Farmer Remarks on Self- Registering Ther^ 

 mometers. Communicated by the Author. 



Sir, 

 I SHOULD not have now thought of troubling you with any re- 

 marks beyond those I offered in a short notice with regard to 

 register thermometers in the last Number of your Journal, had 

 I not since accidentally met with a paper on the subject in an 

 old volume of the Philosophical Transactions^ to which can^ 

 dour requires me briefly to advert. 



Lord Charles Cavendish, to whom we owe some valuable 

 contributions to meteorology in its earliest progress, has de- 

 scribed, in the Traiisactions of the Royal Society of London 

 for J 757,* thermometers adapted for the measure of maximum 

 heat and cold : it would appear that Bernoulli had previously 

 made some instruments for the same purpose, but I am not 

 aware of their nature. The principle, however, which Lord 

 Charles Cavendish proposed, was precisely similar to the one 

 described by Mr King, No. xvi. p. 116, the merit of which I 

 was disposed to attribute to Mr Blackadder, whose account 

 appeared in an early number of this Journal. I feel myself 

 bound, therefore, in rectification of the oversight I had com- 

 mitted, to remark that thermometers acting by the quantity of 

 a column of fluid expelled from the extremity of the tube, ap- 



* Page 300, or Abridgement, vol. xi. p. 138. 



