July 5, 1888] 



NATURE 



22 1 



clouds are seen from here on almost every clear night near 

 the summer solstice. For the last two years special note has 

 been taken of them. In 1887 they were first seen at midnight 

 on June 13, and last seen on July 20 ; this year their first appear- 

 ance at midnight was on June 4, and they are still visible every 

 clear night. The clouds are not, as far as I have observed, 

 coloured, but shine with a pearly or silvery lustre. I have seen 

 them at midnight as high as 30 altitude, but they are generally 

 confined to the first io or so above the northern horizon. The 

 facts that they vary greatly from night to night in appearance, 

 being sometimes almost absent, and that one or two photographs 

 that have been taken of them show them simply as ordinary 

 cirrus clouds, all seem to indicate that they really are very high 

 cirrus lighted by the sun. 



I may add that the upper glows continue to be seen here, 

 though with varying intensity, on every clear night both before 

 sunrise and after sunset, but for the past year no reddish ring or 

 glare has been observed round the sun in the day-time. 



Ben Nevis Observatory, July 2. R. T. Omond. 



Micromillimetre. 



The Council and the Fellows in general meeting have taken 

 into consideration the objection raised by Prof. Riicker to the 

 term micromillimetre. 



This term was in use by microscopists long before the British 

 Association Committee formulated their system of nomenclature ; 

 but nevertheless the Society are unwilling, on a question of 

 precedence only, to insist upon retaining a word which may give 

 rise to confusion. 



The Council have therefore directed the editors of the Journal 

 to discontinue the use of the term "micromillimetre," and to 

 substitute for it that of " micron," which has been in use for as 

 long a time as the former word. 



This resolution has been confirmed by a general meeting of 

 the Society, who agree with the Council in thinking that the 

 term " micrometre," proposed by Prof. Riicker, would give rise 

 to considerable confusion from its similarity to "micrometer." 



Frank Crisp, 



Royal Microscopical Society, June 21. Secretary. 



A Prognostic of Thunder. 



Among prognostics of thunder given in books and elsewhere 

 I have never met with mention of what has for years been to me 

 one of the most trustworthy of weather signs, viz. the formation 

 of parallel streaks or bars, definite in form but limited in number, 

 extent, and persistence, appearing chiefly in cirrus and cirro- 

 stratus, but also oh the surface (apparently) of nimbus. In 

 cirrus they give often almost the first intimation of coming change 

 after settled weather, and are almost, if not quite, invariably 

 followed within twenty four or thirty-six hours by thunder. 

 When they appear on nimbus the interval is much less, but they 

 are not seen, I think, on the thunder-cloud itself. These small 

 patches of definitely marked "parallel bars" are to be distin- 

 guished from the more general parallel arrangement which is 

 often seen on a much larger scale, but which has not, so far as 

 my observation goes, any very distinct value as a weather 

 prognostic. 



As the thundery season is now on, it would be interesting to 

 have the observation confirmed by others, and the connection of 

 this particular form of cloud with electric disturbance explained. 

 I have no doubt of the fact, and have often, and several times 

 within the present year, pointed out these "parallel bars" to 

 friends who had never observed them, and hardly ever has my 

 prediction of thunder failed to come true. In the very few cases 

 in which thunder has not followed in the same locality, I think 

 I may say that there have never been wanting instances of its 

 occurrence within a moderate distance. B. Woodd-Smith. 



Branch Hill Lodge, Hampstead Heath, June 29. 



Parasites of the Hessian Fly. 



Although numbers of these most useful insects were bred 

 last year from puparia of 1886 and 1887, there seemed to be a 

 good deal of doubt among some entomologists as to whether the 

 American species, Merisas destructor, had occurred. I bred a 



large number of various kinds, four of which appeared to me to 

 agree in every respect as to form, colour, and marking with the 

 description given by Prof. Riley. 



During the present month (June) I have bred a very large 

 number of this parasite, specimens of which (both male and 

 female) I sent to Dr. Charles Lindeman, of Moscow, who has 

 just replied that " the specimens of parasites sent, bred in Eng- 

 land from the Hessian fly, seem to me to be Merisus destructor 

 of Riley, &c." He thus fully confirms my opinion of last year, 

 that the American parasite had occurred here. Early in the 

 spring I bred several other parasites which, I am much inclined 

 to think are Platygaster herrickii of Riley ; and, if this is 

 correct, it strengthens the opinion that part of the attack came 

 from America. 



The damp muggy weather appears to be decidedly favourable 

 for the development of " the pest," the larvae of which I found 

 at the beginning of this week engaged in weakening the stems 

 of barley ; and on June 2 I observed a female Hessian fly ovi- 

 positing. The number of eggs laid was 158 ! Truly a most 

 prolific " pest," requiring both natural and artificial means to 

 check its increase. F. E. S. 



Fact and Fiction. 



As Mr. Grant Allen reads Nature, — indeed this is evident 

 from a sentence in his novel "This Mortal Coil," now in course 

 of publication in Chambers' Journal — he will perhaps be good 

 enough to satisfy my doubts upon the following practical points 

 in electro- and thermo-physics. Firstly, in order to successfully 

 attract a flash of lightning to a tree, is it necessary to bury 

 beneath its roots a Rhumkorf coil ? Secondly, do Rhumkorf 

 coils exist which are without secondary wires ? Thirdly, will an 

 electric discharge ignite commercial petroleum oil ? 



While it is not undesirable that scientific fact should be 

 imported into modern fiction, it is surely important that it should 

 be fact : loose statements are apt to perpetuate themselves. 



Mr. Allen is exceptionally well read and observant, and I am 

 quite at a loss to understand why a simple solution of continuity 

 in that part of his copper conducting wire which was immersed 

 in the petroleum would not as well have served his purpose (if 

 indeed, that purpose could have been effected in the way 

 described), as the elaborate expedient of burying and destroying 

 an expensive piece of apparatus. 



Dublin, July. Harry Napier Draper. 



The Nephridia of Earthworms. 



The number of Nature published on June 28 last contains 

 (p. 197) an interesting paper by Prof. Baldwin Spencer, which 

 deals with the excretory system of the gigantic Australian earth- 

 worm Megascolides. Prof. Spencer promises an extended 

 memoir upon the anatomy of this earthworm, which has not 

 hitherto received more attention than a superficial description. 

 In the meantime the paper in Nature contains an abstract of 

 the results obtained by the author from his investigation of the 

 nephridia. 



This paper is particularly interesting to myself, as I am at 

 present preparing an account of some further investigations into 

 the anatomy of the excretory system of earthworms, which will 

 supplement those already published by me in the Quart. J our 11. 

 Micr. Sci. (January 1888). 



It appears from Prof. Spencer's paper that, as he himself 

 points out, there is a considerable resemblance between the 

 excretory organs of Megascolides and of Perichceta aspergillum, 

 one of the species investigated by me ; there are at the same 

 time certain important differences between the two types. 



In my paper upon P. aspergillum I described only the 

 nephridia of the anterior segments of the body. I have since 

 found that the nephridia of the posterior segments are in some 

 respects different. In both cases, however, the external orifices 

 are more numerous than I was at first inclined to suspect. They 

 are not limited to the area of the segments which lie between 

 the setae, but are found all over the body, scattered irregularly ; 

 they have, in fact, no relation whatever to the segmentation oj the 

 body. 



The tufts of tubules in the posterior segments of the body are 

 not so abundantly developed as in the anterior segments, where 

 they not only form a layer covering the body-wall and septa 

 but occupy nearly tl e whole of the ccelomic space available. 



