182 



KNOWLEDGE. 



[AUODBT, 1902. 



jirobable that tli»> sonilm- niatorial of tlic t'unniT as it 

 overtaki's the red s|M«t is ilriftccl !il)ni]itl_v southwards, 

 Mowing' alon^' its soiitliern honlurs and then on reafhini; 

 the /'. side of the latter it turns sliarply to north and thus 

 occu])ies the same latitude both east and west of the n' I 

 spot. The/. end of the .south trojiical (or temperate) nia^s 



Red Spot and it« Surroundings. 



will come up to the /. I'ud of the red spot at the be^in- 

 nin;„' of September, and it will be important to ascertain 

 whether the extremity of the former flows southward. 



Telescojiic observers should keep a diligent watch during 

 ensuing months on the developments in this exceedingly 

 interesting region of Jupiter. 



Between 1900, September, and 1902, June, the mean 

 motion of the red spot conformed precisely with the 

 period of 9h. 55m. 40-6s. on which System II. of the 

 ephemerides is based, for its longitude remained con- 

 sistently at 44fi°. Lately, however, the spot has indicated 

 a slight acceleration in velocity, for its longitude appears 

 to have decreased 2° or 3°, and it is likely that it will show 

 a further decrease in succeeding months, for the past 

 history of the spot sufficiently proves that it is liable to 

 some marked fluctuations in its rate of motion. 



Bishopston, Bristol, W. F. Denning. 



1902, July 4th. 



A MODERN TYCHO. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — My attention has been called to an article by 

 Mr. E. Walter Maunder in your issue of May, 19u2, 

 entitled "A Modern Tycho," in which the following 

 sentence occurs : — " Jey Singh does not seem to have 

 effected any reformation of the Indian calendar, and his 

 observatories, despite their great size, cannot have been 

 of much value for really scientific work." 



I would ask your correspondent if he has ever seen an 

 account of the " Zeech Mahommed Shahi," or Jey Singh's 

 astronomical tables, published by him, after years of 

 observation at his observatories, about 1728. In the 

 preface to these tables Jey Singh states that the old 

 Siddhantas give incorrect results, that at Mahommed 

 Shah's request he had erected several observatories, and 

 that after many years' labour he had succeeded in jjroduc- 

 ing these tables according to the preaiction of which the 

 celestial phenomena take place exactly. He also adds 

 that hearing astronomical observations were being made 

 in Europe, he had sent thither to make enquiries, and that 

 as a result he had obtained the tables of de la Hire, which 

 on examination proved very inaccurate. There is an 

 account of the " Zeech Mahommed Shahi," by Dr. W. 

 Hunter, in " Asiatic Researches," Vol. V., but, as far as I 

 know, these tables have never been thoroughly examined 

 by an expert with a view to test their accuracy. I was 

 informed the other day by a native astronomer, fairly well 

 acquainted with the modern methods of practical astro- 

 nomy, that these tables generally give results not often 

 more than two to four minutes in error. If this is so, Jey 

 Singh's work must have been of a high order, and of con- 

 siderable scientific value. I hope to obtain a complete 

 translation of these tables shortly, and have them properly 

 investigated by acomjieteut expert. 



But, putting aside the question of the accuracy of these 



tables, there is no doubt that some of Jey Singh's astro- 

 nomical measurements are as ))reci8e as have ever been 

 attained by naked-<'ye work. The ini'lination of the fa<-e 

 of the gnomon of the big instrument at Jeypore is within 

 a minute of arc of its correct value. Jey Singh's deter- 

 mination of the latitude of Jeypore and tijjain are 

 certainly within half a minute of the truth, and |)0S8ibly 

 even closer, while the value he deduced for t]u- obliquity 

 of the ecliptic is of an equally high order of accuracy. 

 The value he gives for the average annual procession is, if 

 my memory serves rae right, within a second of the modern 

 determination. 



During last summer I was engaged in restoring the 

 observatory at Jeypore, and had ample opportunities for 

 testing and investigating the instruments. Their accuracy 

 was shown by the excellent agreement in the results 

 obtain^'il by observing altitudes, azimuths and declinations 

 with different instruments. Jey Singh was a good mathe- 

 matician, and wrote many works on astronomy and trigo- 

 nometry. Under these circumstances it seems probable 

 that the " Zeech Mahommed Shahi " are a very great 

 improvement on the old Siddhantas, though possibly not 

 possessing the accuracy wliich Jey Singh claimed for them. 



Mr. Maunder writes rather disparagingly of Jey t<ingh, 

 who, as I have shown above, certainly obtained very good 

 results, and did the best he could for the advancement of 

 astronomy with the limited means at his disposal. It 

 should be remembered too that Jey Singh lived in very 

 troubled times, and that the very existence of his State was 

 constantly being threatened both by enemies from without 

 and intrigues from within. Indeed, considering the state 

 of affairs at the time, it is wonderful that Jey Singh ever 

 found leisure for the erection of his observatories, and the 

 writing of his books. ^_ j,p_ Garrett, Lt. R.E. 



India, June, 1902. 



[I had no wish to disparage Jey Singh, who, as Mr. 

 Garrett most truly says, lived in very troubled times in 

 the which it was wonderful that he found the opportunity 

 for accomplishing so much scientific work. But I think 

 that Mr. Garrett has missed the point wliich I was really 

 anxious to make. I have only had the opportunity of 

 myself examining one of Jey Singh's observatories — that 

 of Delhi — but I was much impressed with its limitations 

 for really good observational work. The gnomon, after all, 

 despite its great size, would have given no better deter- 

 minations of time than a comparatively small sun-dial, 

 while the circular buildings only permitted the observation 

 of altitudes and azimuths of objects when low down, and 

 I saw no indication that any great care was taken about 

 the precise position of the observer's eye. 



And the accuracy with which the various buildings are 

 placed — as, for exampile, the inclination given to the face of 

 the gnomon — so far from bearing witness to any improve- 

 ment effected by the observatories, is proof just the other 

 way. For Jey Singh must have determined the latitude 

 of the jilace with this precision before ever he started to 

 build ; he could not have altered his gnomon afterwards. 

 For this purpose he probably used quite a simple apparatus 

 of poles fitted with sights ; and it was the superior efii- 

 ciency and range of usefulness of just such simple means 

 that I had chiefly in view in my paper. Jey Singh's 

 observatories are most certainly interesting, but they are 

 scarcely practical. 



I am glad to note that Mr. Garrett hopes to obtain a 

 complete translation of Jey Singh's tables ere long ; but 

 I venture to think that it would be of even greater interest 

 to astronomers if he would himself undertake a series of 

 observation of stars and planets with the .Jeypore instru- 

 ments as they stand. — E. Walter Maunder.] 



