214 Annals of the Philosophical Club 



of Edinburgh was also discussed, in which he maintained 

 that the small globules of liquid, constituting fog and 

 clouds, are invariably formed round minute particles of 

 dust or other solid matter suspended in the air. Professor 

 Tyndall expressed great doubts in regard to Mr. Aitkens's 

 contention, for his own observations had convinced him that 

 dense clouds can be produced in optically pure air. Without 

 denying that such particles may promote the condensation 

 of vapours, he did not hold this to be necessary in the 

 formation of fogs or clouds. 



Feb. I7th, 3O4th meeting. Mr. Balf referred to a recent 

 discussion at the Royal Society, in which the presence of 

 fish in the hot springs of the Sahara was treated as an 

 established fact, though he thought it required further 

 investigation. Last winter he visited the Fontaine Chaude, 

 a mineral spring near Biskra in the Sahara, in which the 

 waters have a temperature of 108 to 110 F., and fish of 

 the genus Cyprinodon are said to live. He was, however, 

 assured by the official (Arab) custodian that the fish never 

 came directly from the spring into the reservoir, but are 

 found further down in the rivulet which flows from it. 

 Still, as this, like so many streams of the Sahara, is lost 

 in the sand, it is difficult to explain their presence in it. It 

 may be connected with another fact, which appears to rest 

 on the testimony of competent observers such as Charles 

 Martins, that minute fish had been observed in water 

 brought up from great depths by artesian wells newly 

 opened in the Sahara. Dr. Asa Gray 1 (guest) said that 

 somewhere in the United States springs frequently brought 

 up small fish with leaves. Sir J. Hooker had heard of fish 

 inhabiting hot springs in the Himalayas, and Mr. Moseley 

 had seen goldfish thriving in the hot springs at Bath, and 



1 Dr. Asa Gray, born on Nov. i8th, 1810, at Paris, New York, after 

 taking the degree of M.D., devoted himself to the study of botany, and for 

 fully thirty years was Professor of Botany at Harvard. He was a strong 

 but not uncritical supporter of Darwin's views on the ' Origin of Species, ' 

 and wrote important books on the flora of North America, besides numerous 

 special memoirs. Justly ranked among the leading botanists of his time, 

 he died Jan. soth, 1888. 



