Rev. J. Challis on the Aberration of Light. ^ 3 93 - c 



see whether some of the works of Kepler, which Prof. Friscti " 

 could not discover in Germany, might not be found in our 

 libraries, which certainly are surpassed by the richness of 

 especial departments of those of the respective countries; and 

 none would expect, for instance, to find more Austrian Incu- 

 nabula in English libraries than there are in Vienna, &c. But 

 taking the biographical opulence at a fair average, the balance 

 will not be unfavourable for this small and insulated empire. 

 The very first glance I cast in the Catalogue of the British 

 Museum (even in its present transitory state) was encou- 

 raging, as I found No. 5 of Prof. Frisch's Desiderata. The 

 full title of this little rarity is as follows : — " Joannis Kepleri 

 Mathematici ad Epistolam Clarissimi Viri D. Jacobi Bartschii 

 Laabani Medicina? Caiididati Prcefixam Ephemeridi in anno 

 1629 Responsio : de Computatiohe et Editione Ephemeridum, 

 Typis Saginensibus 1629." It is a small 4to pamphlet of 

 only eleven pages, printed on paper and with a type of the 

 then current publications of the day. The conclusion is so 

 characteristic of the man, that we shall translate it: — "But 

 while the storm is raging, and the shipwreck threatens public 

 affairs, nothing remains to us but to let the anchor of our in- 

 nocuous studies go down to the profound of eternity ! Given 

 at Sagan in Silesia, with our own types, anno 1628." It 

 is known that Kepler had been in some relation with the 

 great Wallenstein, and the place of printing is one of the pos- 

 sessions of the great warrior, he having been Duke of Sagan. 

 The name of the duke is also mentioned in the contents of 

 the work. 



London, April 15, 1846. 



LXIV. On the Aberration of Lights in Reply to Mr. Stokes. 

 By the Rev. J. Challis, M.A., Plumian Professor of As- 

 tronomy in the University of Cambridge. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 T HAD reason to expect, when I made my last communica- 

 -*- tion on the Aberration of Light, that I should not have 

 occasion to trouble you again on this subject. Mr. Stokes's 

 remarks in the April Number compel me to say a few words 

 more. 



I can assure Mr. Stokes that I take the aberration of light 

 in its usual acceptation, and I have no doubt that he does 

 also. The difference between us is not in the thing explained, 

 but in the principles of our explanations. My explanation, 

 which is very simple and brief, being entirely contained in 

 Phil Mag". S. 3. Vol. 28. No. 188. May 1846. 2 E 



