518 Chronicles of Science. [Oct., 



for many of the observed peculiarities of comets, yet it appears to 

 us not unlikely that a way may yet be found to reconcile the strange 

 phenomena which some comets have presented with the views 

 maintained by Professor Tyndall. We cannot at present admit 

 his explanation of lateral streamers, because it leaves us in quite 

 as much perplexity as we have ever been in with respect to this 

 strange phenomenon. When we see a tail extending in a right 

 hne from the head, but at an angle of 60'^ or so to the radial line 

 from the sun, we require more to account for the pecuHarity than 

 the bare possibility that along that line the actinic rays may 

 temporarily have obtained the mastery ; and when we see, as in the 

 famous comet of 1774, six distinct tails spreading from the head 

 in the shape of a fan, it is yet more unsatisfactory to refer to a 

 mere possibility of this sort. Professor Tyndall mentions no 

 illustrative case as having occurred in the course of his experiments 

 on actinic clouds ; and therefore, so far as this part of his theory 

 is concerned, he seems scarcely justified in saying that " throughout 

 he has dealt exclusively with true causes," and that " no agency 

 has been invoked which does not rest on the sure basis either of 

 observation or experiment." 



However, the great difficulty in cometic phenomena, the apparent 

 swinging round of the tail with a velocity often far exceeding the 

 greatest velocity possible within the solar scheme, is undoubtedly 

 mastered by Professor Tyndall's theory; and this circumstance 

 renders us hopeful that he may be able to find a more satisfactory 

 explanation than he has yet given of abnormal cometic phenomena. 



The application of the enormous heat-gathering powers of the 

 great Parsonstown reflector to the solution of the long-vexed 

 problem of the moon's heat, is one of the most valuable results 

 which have followed the construction of clock-work suited to drive 

 this great telescope. The question is one of such extreme delicacy, 

 that so long as the telescope had to be guided by the old arrange- 

 ment no results of a satisfactory nature could be hoped for. On 

 the other hand, no other telescope could be apphed to the work 

 with reasonable chance of success. Mr. Huggins had detected no 

 sign of heat, when the moon's rays were gathered by his powerful 

 refractor upon the face of a delicate thermopile ; and indeed Pro- 

 fessor Tyndall long since pointed out that it was almost hopeless 

 to apply a refractor to such work, the moon's heat being of such 

 a nature that far the greater part must be absorbed by the object- 

 lens. With the Kosse telescope (used in combination with a delicate 

 thermopile), clear signs of heat were detected, and thus at length 

 the question has been set at rest. 



Comparing the heat received from the moon with that derived 

 from several terrestrial sources, Lord Rosse has deduced the con- 

 clusion that at the time of full moon a part of the moon's surface 



