Junk. 1911. 



KNOWLEDGE. 



245 



Herschel himself states " A forty-feet telescope should only be 

 used for examining objects that other instruments will not 

 reach." "The opportunities of using the forty-feet are 

 rendered very scarce." On August 28th. 1789, he says 

 " Having brought the forty-feet to the parallel of Saturn. 

 1 discovered a sixth satellite of that planet, and also saw the 

 spots upon Saturn better than 1 had ever seen them before, so 

 that I may date the finishing of the forty-feet telescope from 

 that time." 



This is great praise for the big instrument, but Dr. Dick in 

 describing the details of its construction and worl<, as published 

 in the Phil. Trans., says: " It was not to be expected that a 

 speculum of such large dimensions could have a perfect 

 figure imparted to its surface nor that the curve, whatever it 

 might be, would remain identically the same in changes of 

 temperature ; therefore we are not surprised when we are 

 told that the magnifying powers used with this telescope 

 seldom exceeded two hundred ; the cjuantity of light collected 

 by so large a surface being the principal aim of the maker." 

 The Practical Astronomer, Page 304. 



No doubt Herschel's object was chiefly to get as much light 

 as possible out of his instruments, as he was constantly 

 searching for faint nebulae, minute satellites and so on. 

 Thus we often find him adopting contrivances, and using 

 expedients to obtain the maximum " penetrating power." 



Possessing optical and mechanical sicill only matched by- 

 unwearying energy, Herschel must have succeeded in pro- 



ducing some thoroughly good instruments, though it should 

 never be forgotten that his splendid ob.scrvational work more 

 indicates the measure of the man than the particular kind or 

 quality of his glasses. 



We, at the present day, cannot fairly judge as to the degree 

 of perfection he attained, but it certainly ni'ist have been 

 considerable. Critics may possibly find fault with a few details 

 recorded in his papers, in the volumes of the Phil. Trans., 

 such as the supposed discovery of the ring around Uranus, but 

 when we consider the enormous amount of work he accom- 

 plished, sometimes in indifferent air, or amid trying circum- 

 stances, he must have been more than mortal could he have 

 invariably avoided mistakes. 



Herschel's papers number sixt>'-nine, and they are practically 

 inaccessible to the general astronomical pulilic, in the volumes 

 of the Phil. Trans. Will these important memoirs ever be 

 reprinted in book form ? 



Every year brings us some new astronomical works, but 

 they are neither so welcome nor so valuable as a volume of 

 Herschel's writings would prove. And this has been a 

 desideratum for more than a century 1 Had Herschel's 

 collected papers been available for convenient reference what 

 immense trouble would have been avoided, and how many 

 misunderstandings prevented ! Some descendant of the 

 illustrious astronomer should present the scientific world with 

 a handy volume of his results described in his own language. 



SOL.AR DISTL'RB.VNCES UURIXG APRIL, 191 1. 

 Bv FRANK C. DENNETT. 



There has been a continuance of the somewhat increased 

 activity upon the solar disc. On three days, April 18th, 19th 

 and 20th, no disturbance, bright or dark was visible ; and upon 

 the 16th and 17th only bright, or faculic disturbances were 

 seen. At noon on April 1st the longitude of the central 

 meridian was 188° ib' . 



No. 12 on the March list continued upon the disc until .Vpril 

 6th, and therefore re-appears upon the present chart. 



No 13. — Near the eastern limb, on the 1st. there appeared a 

 moderate spot, but when farther on the disc it was seen to 

 consist of three spotlets and three pores in slightly divergent 

 lines. The middle, largest spot had the inner edge of its 

 penumbra fringed brightly. The members decreased from 

 the 6th until the 8th when only penumbraless pores were 

 visible having a faculic lip. The length of the group was 

 44,000 miles. The region was faculic until the limb was 

 reached. 



No. 14. — A spotlet. only seen upon the 2nd. 



No. 15. — A pore, only visible upon the 4th. approximately 

 in the position shown. 



No. 16. — A solitary spot, 10,000 miles in diameter, crossed 

 tte disc between the 3rd and 15th. The inner edge of its 

 penumbra was fringed bright upon the Sth. 10th and 12th. 

 whilst the umbra was crossed by a bridge upon 12th and 13th. 



.No. 17. — A spot, 14,000 miles in diameter, visible from April 

 22nd until May 3rd. The penumbra brightened inwards upon 

 the 24th, 26th, 27th, 30th, and May 1st, and the umbra was 

 crossed by a bridge on the 24th, and from the 27th until the 

 30th. On the 2Sth and 29th the southern half of the umbra 

 appeared to be less dark than the northern. 



No. 17(7. — \ fine spot 15,000 miles across, visible from 

 .4pril 22nd until May 5th. The brightening inwards of the 

 penumbra was noted on the same days as No. 17, and also 

 on the 26th. The umbra was ci"ossed by a bridge w-hich 

 became very narrow. .\ faculic chain, convex northward, 

 joined Nos. 17 and 17a, in which evanescent pores appeared 

 on the 28th and 29th. 



No. 176. — A spotlet seen from the 22nd until May 2nd. 

 There was a bright inner fringe to the penumbra on the 24th. 

 On the 27th the umbra became elongated and on the 28th and 

 29th broken. Pores showed round it on the 27th, 28th, 29th, 

 and on May 1st. 



No. 17c. — Two spotlets upon the 24th. one remaining until 

 the 26th. 



No IS. — A small group of pores only seen upon the 30th. 



The chart is constructed from the combined observations 

 of Messrs. J. McHarg. A. A. Buss, E. E. Peacock, and E. C. 

 Dennett. 



DAY OF APRIL. 



