Prof. Tyndall on Recent Researches on Radiant Heat. 257 



my caustic potash, and of pure glass for my sulphuric acid. But 

 with these also a long time elapsed before I was master of the 

 anomalies which from time to time made their appearance. The 

 dust of a cork ; a fragment of sealing-wax, so minute as almost 

 to escape the eyesight ; the moisture of the fingers touching the 

 neck of the U-tube, in which the sulphuric acid was contained 

 — these, and many other apparently trivial causes, were sufficient 

 entirely to vitiate my results in delicate cases, giving me on 

 many occasions effects which I knew to be large multiples of 

 the truth. Thus, while perfectly safe as regards the stronger 

 gases whose energy of action masked small errors, prolonged 

 experiment was needed to connect these with the feebler ones, and 

 to refer them to air as a standard. In short, I thought it due 

 both to the public and myself to abstain from giving more than 

 a clear general account of my inquiry until I had mastered every 

 anomaly that had arisen. I cannot regret having exercised this 

 patience, more especially when I find one of the ablest and most 

 conscientious experimenters of modern times falling, as I believe, 

 into error on some of the points which most perplexed me. 



A few weeks subsequent to the receipt of my paper by the 

 Eoyal Society, that is to say, on the 7th of February, 1861, an 

 account of experiments on the transmission of radiant heat 

 through gases was communicated by Professor Magnus to the 

 Academy of Sciences in Berlin. In this inquiry the absorption 

 of heat by vapours was left untouched, nor did it embrace the 

 reciprocity of radiation and absorption which my investigation 

 revealed. But as regards absorption by gases, Professor Magnus 

 and myself had operated on the same substances ; and consider- 

 ing the totally different methods employed, the correspondence 

 between our results must be regarded as very remarkable. 



Previous to occupying himself with the transmission of heat 

 through gases, Prof. Magnus had made an investigation on the 

 conduction of heat by gases, and he was led naturally by this 

 inquiry to take up the question of gaseous diathermancy. My 

 knowledge of his great skill and extreme caution as an experi- 

 menter entirely ratifies a statement which he has repeated more 

 than once in his published memoir, namely, that his results on 

 the diathermancy of gases were already obtained at the time he 

 communicated his results on conduction to the Academy of 

 which he is a member, that is to say, in the month of July 

 1860; in fact the very experiments intended to determine their 

 conduction, really revealed the absorption of the gases. I am 

 quite persuaded that the results of Prof. Magnus are inde- 

 pendent of mine, and that, had I published nothing on the sub- 

 ject, his own inquiries would have led him to the discoveries 

 which he has announced. That my researches preceded his by 



