236 



KNOWLEDGE. 



[December 1, 1892. 



that, at the rate of 5800 descriptions of new species 

 per annum, it -would requii-e 340 years merely to describe 

 all the undescribed species of insects ; and the description 

 of a species is'only the beginning of our knowledge of the 

 insect itself in its perfect state. Every species would 

 requii'e many volumes before its life-history, habits, 

 anatomy, physiology, and relations to other species could 

 be dealt with, with auythmg like completeness. All that any 

 entomologist can accomplish is to add what he can to the 

 gradually accumulating stores of knowledge in the special 

 department of entomology to which he is best able to 

 devote himself by study and inchnation. 



In England we have about 12,000 species of insects, and 

 it is perhaps not to be expected that the ultimate total, 

 when all the smallest species have been collected and 

 studied as assiduously as the larger ones, will exceed this 

 estimate by more than a few hundred, or at most one or two 

 thousand. But with foreign countries it is very different ; 

 and I must confess that I was surprised, when I lately 

 received a fine new species of Pha.s}i)ida, from Madagascar, 

 to find that barely half-a-dozen species had yet been 

 recorded from that island. And yet the Pliasniida, or 

 stick insects, are among the largest insects. They are 

 generally conspicuous, and easily collected, and Mada- 

 gascar is an island from which large collections of insects have 

 repeatedly been received of late years ; and yet our know- 

 ledge of this group of insects as occurring in the island is 

 practically nil .' If this is the state of our knowledge of 

 such insects as Phasmidtt, how imperfect must it be of the 

 smaller species of Coleoptem, Hiiiiiennptera, Dipttrd, &c., 

 many of which are of almost microscopic dimensions ! 

 Many insects are so local and so closely connected with 

 plants which disappear before civilization, that the same 

 fate of extermination which has fallen on so many of the 

 larger animals dui-ing the last century cannot but fall 

 heavily upon these also. It is not too much to say that it 

 is highly probable that a large proportion of the insects at 

 present existing in the world will become extinct before 

 their existence is even known to scientific men. 



Yours faithfully, 



W. F. KiRBY. 



THE 'WILSOX PliEXOMEXOX" OF SOLAK SPOTS. 



To the Editor of Knowledge. 



Slr. — In his valuable work, " Anleitung zur Durch- 

 musterimg des Himmels," published in 1880, Dr. Klein 

 states (page GO) that Wilson was anticipated m his obser- 

 vation of the phenomenon of the varying position of the 

 umbra in the penumbra of a solar spot as it passes across 

 the disc by Maximilian Ludwig Christoph Schiilen, of 

 Essingen, in ^Y^irtemberg, and this statement is adopted 

 in the last edition of Webb's " Celestial Objects for Common 

 Telescopes.'"" It is, however, foimded on a mistake, the 

 source of which is easy to trace. Wilson was first led to 

 his ^iew that the solar spots were depressions in the photo- 

 sphere by observations of a great spot which appeared in 

 isovember, 1769, and he at once communicated his per- 

 ception of the phenomenon now usually called by his name 

 to the London Chronich'. But he did not send his paper 

 on the subject (in which later observations confirming his 

 view are communicated) to the Eoyal Society until 1773, 

 and it appears in the P/tilosojiliical Transactions for 1774. 

 No doubt it was by that that foreign astronomers obtained 

 knowledge of his observations. Schiilen's (in which he 

 also noticed, he tells us, the funnel-shaped appearance of 

 several spots i were made m the summer of 1771, and com- 



* In that work Schiilen's name appears en-oneously as Schiiler. 



municated first to a newspaper in Stuttgart, the substance 

 afterwards appearing in papers in Switzerland and other 

 places. From that time he heard no more of the matter 

 until, in 1777, he was surprised to see in a French pub- 

 lication the discovery mentioned and ascribed to Wilson. 



The Eev. F. Wollaston, and also Lalande, expressed 

 their dissent from Wilson's views on the groimd that the 

 phenomenon in question is not aJicai/s seen. He replied 

 in the Phihisophical Trans(U-tionii for 1783 ; and surely the 

 objection was insufficient, as some penumbne might be 

 much shallower than others, too shallow indeed to show 

 the phenomenon in question. It does not appear that he 

 ever heard of Schiilen's observations. The latter pub- 

 lished at Nordlingen, in 1782, a small treatise under the 

 title " Beitriige zur Dioptrik und Geschichte des Crlases," 

 in which he narrates the facts above mentioned respecting 

 his own observations, evidently unaware that Wilson had 

 reaUy anticipated him by more than a year. 



As to the phenomenon itself, it is well known that that 

 most persevering and careful sunspot observer, the Kev. 

 F. Howlett, has not in his long course of observations, 

 now extending over thirty-five years, recognized any such 

 funnel-shaped appearance. A letter appears from him on 

 this subject in the number of Knowledge for September, 

 1889, and it is open to any Fellow of the Eoyal Astronomical 

 Society to study the long series of sunspot observations 

 I presented by him to the Society. 



i What are we then to conclude '? It appears to me that 

 I the case is one of those in which a perception given from 

 observations made with small instruments and low powers 

 fails to be seen under the application of larger instruments 

 and higher powers, which furnish clearer and more distinct 

 images of matters of detail ; and this is also the view of 

 Dr. Klein. 



Schiilen's observatioris, it may be remarked, were made 

 with a non-achromatic telescope of 13^ feet focal length, 

 using a power of about 100. Wilson's telescope was a 

 Gregorian reflector of 26 inches focus, which magnified 112 

 times. I need hardly refer to the way in which Mr. 

 Howlett's observations have been made, and how it enables 

 his drawings to bring out the minute details of the spots 

 and their surroimdings. We must surely concede that the 

 peuumbral depression is, in the vast majority of cases, 

 exceedingly shallow. 



Yours faithfully, 

 Blackheath, November 7th, 1892. W. T. Lwn. 



THE LIFE-HISTOKY OF STARS. 

 To the Editor of Knowledge. 



Sir, — Yarious theories as to the evolution of stars and 

 theu' subsequent decadence have appeared fi'om time to 

 time, but they have hitherto been purely theoretical. It 

 seems to me that observation can throw some light on the 

 question ; and as far as I have been able to foUow its 

 guidance, this light leads in a rather unexpected direction. 



A star cooling down will of course fade away gradually, 

 and as the last light which a cooling body emits is red, it 

 was at one time sitpposed that red stars were in this state 

 of decadence. It seems pretty certain, however, that red 

 stars owe the colour of their light not to then- low tem- 

 perature, but to absorption by an intervening medium. 



The best observational test seems to me to be this : If 

 a star has cooled down, and lost a considerable part of its 

 light, it will probablj' be nearer to us than other stars of 

 the same magnitude ; for if its original light was restored, 

 its magnitude would be considerably mcreased. And if 

 the class of stars which give a particular kind of light are, 

 in the average, nearer to us than stars of the same mag- 



