216 



point out the essential distinctions between Professor Forbes's and 

 Dr. Tyndall's theories respecting the laminar structure. A disposi- 

 tion had recently manifested itself to confound the two theories, 

 whereas they were so fundamentally different, that the physical rea- 

 soning essentially involved in the one was totally inapplicable to 

 the other. The differences were such as could not be ignored, 

 if we would hope to arrive at a complete and final view of the 

 subject. 



The remarks in this lecture, Mr. Hopkins said, had been made 

 with a sincere desire of eliciting the truth, and not in the mere spirit 

 of advocacy of preconceived opinions ; nor would it, he conceived, be 

 inconsistent with this assertion if, in conclusion, he reminded those 

 who were interested in the subject, that though his own investiga- 

 tions nearly fifteen years ago respecting the internal pressures and 

 tensions of glacial masses were little noticed then, and had been little 

 mentioned more recently, no one had ever attempted to refute them ; 

 and now, on the contrary, all those observations and experiments of 

 Dr. Tyndall which related to this part of the subject, and were at 

 present generally received, were entirely confirmative of them. The 

 nature of the reasoning which has now been applied to the subject, 

 whether founded on analogies with certain phenomena of lamina- 

 tion, or on thermal principles, clearly proved the necessity of more 

 accurate conceptions of these internal pressures and tensions than 

 could ever be acquired from merely elucidatory experiments. 



May 30, 1859. 



" On the Occultation of Saturn by the Moon on May 8, 1859." 

 By Professor Challis. 



In observing this occultation, Professor Challis was prepared to 

 take especial notice of the occurrence of any phsenomenon like that 

 witnessed at the occultation of Jupiter on January 2, 1857, on which 

 occasion the disc of the planet at emergence was seen to be traversed 

 by a dark band contiguous to the moon's limb. No such appearance 

 was visible in this instance. The circumstances of the reappearance 

 of Saturn at the moon's bright limb on May 8, were very similar to 

 those of the reappearance of Jupiter, excepting that there was no 

 depression of the limb where Saturn reappeared such as that which 

 was noticed at the place of Jupiter's reappearance. The comparison 

 of the two occultations seems, therefore, to indicate that the phseno- 

 menon seen in the case of Jupiter was in some way connected with 

 the indented form of the moon's limb. 



