60 LIFE AND EXPERIENCES CHAP. 



vacations in the years 1859-62 in working with 

 Bunsen on photometrical measurements ; and the 

 results were printed in German in Poggendorfs 

 Annalen and in the Philosophical Transactions in 

 English. An appreciative reference was made to 

 these researches by Ostwald in an appendix to his 

 reprint in his Collection of Scientific Classics. 



"The Photo-Chemical researches of Bunsen and Roscoe 

 deserve the name of a classical investigation, as they not only 

 have gathered together all points known hitherto on the 

 subject, but by their wide and thorough experiments have 

 laid the foundation for all further work on the subject. It 

 cannot be doubted that these researches not only serve as a 

 classical, but as the classical type for all future experimental 

 work on the subject of Physical Chemistry. 



" In no other research in this domain of science," he adds, 

 " do we find exhibited such an amount of chemical, physical, 

 and mathematical dexterity, of ability in devising experi- 

 ments, of patience and perseverance in carrying them out, of 

 attention given to the minutest detail, or of breadth of 

 view as applied to the grander meteorological and cosmical 

 phenomena of nature." 



In this connection the following (translated) letter 

 from Bunsen is of interest. It requires a word or two 

 of explanation. On my return to England from Heidel- 

 berg for the Christmas holidays, 1855-6, I heard for 

 the first time of Draper's previous work on a chlorine 

 and hydrogen " tithonometer," and, somewhat down- 

 cast by this discovery, I wrote to Bunsen on the 

 subject. His wise and encouraging words put new 

 heart into me, and I returned to work at Heidelberg 

 determined to do my best to prove equal to the task 

 that lay before me. 



HEIDELBERG, \ith January, 1856. 

 MY DEAR ROSCOE, 



I think that Draper's experiments will not require to be 

 repeated by us any more than Witwer's. Independently of 

 much that appears to me to be inexplicable in them, the 



