470 Scientific Gleanings. 



ancient Greets, expressed in the mathematical forms which they 

 devised, has been an important element in the formation of that 

 astronomy of modern times of which I have several of the eminent 

 masters near me. And this connected progress of knowledge 

 from ancient to modern times has been exemplified in various 

 portions of science, and still goes on appearing in new examples. 

 You recollect, perhaps, that a Roman philosopher, Seneca, made 

 a remark which, though conjectural, is striking. In speaking of 

 comets, he said, these objects now appear to follow no law, as the 

 planets do. They appear unforeseen and unexpected, filling us 

 with perplexity and alarm. Yet these bodies, too, he said, shall 

 disclose their laws to astronomers in future years. Their returns 

 will be predicted, their laws known, and our posterity will wonder 

 that we did not discern what is so plain. And this prophecy has 

 been fulfilled. Comets have had their returns predicted, and have 

 fulfilled their predictions. And though this is not always the 

 case, for comets still shine forth unpredicted and unforeseen, yet 

 still, even in such cases, we are not quite destitute of knowledge 

 of their law and progress ; for when an unexpected stranger of this 

 class blazes forth in our sky, as soon as he has shown himself for 

 a few days, we can mark the path which he will follow, the rate 

 at which he will travel, and in a great degree the appearances 

 which he will assume. And even objects which as yet are still 

 more lawless and perplexing to our science than comets are, 

 still not altogether extraneous to the domain of our know- 

 ledge. There is a class of such objects which has been especially 

 attended to by the British Association. This is the subject of the 

 first of the communications which are to be laid before this Sec- 

 tion to-day. I speak of Prof. Powell's " Report on Luminous 

 Meteors." These objects, falling stars, shooting stars, fiery globes, 

 or whatever tbey may be commonly called,- have attracted the 

 attention of this Association for many years ; and the Report 

 which we are to have laid before us to-day is the continuation of 

 several Reports of the same kind prepared by the same gentleman 

 in preceding years. These bodies, as I have said, are in a great 

 degree irreducible to laws and extraneous to our science; yet not 

 wholly so. We have speculations of ancient times by some of 

 our most eminent philosophers, in whieh these bodies play an 

 important part. Prof. W. Thompson has been led, by his 

 mathematical speculations on Heat, to the conclusion, that the 

 heat of the sun is maintained by the perpetual falling in upon 



