Oct. 13, 188 1] 



NATURE 



557 



ber 10, in a gathering of pond-water made in this neighlourhood 

 and brought home for microscopical examination, a somewhat 

 nngular and unu-ual object presented itself, but speedily making 

 its way to the sediment at the bottom, it became lo.t to sight. 

 Upon the evening of the 12th, or after the lapse of fully two 

 days, while holding the bottle to the light, the same object again 

 appeared, swimming or flying in mid- water with a pecidiar jerl.y 

 movement resembling that of some of the Entomostraca, and 

 for one of which I at first mistook it. On removal by means of 

 a dipping-lube to a zoophyte trough for fuller examination, it 

 proved, to my ^reat surprise, to be one of the small Hymeno- 

 pterous flies of the Proctotrui-id family, and here it continued 

 its active movements, now « alking and running upon the bottom 

 and sides of the trough, now flying, as it were, through mid- 

 water by the energetic movements of its wings, but apparently 

 making no effort to ecape. Examination thus proving no easy 

 task while living, and fearing the loss of a specimen of habits 

 so unique, I decided upon securing it permanently ns a micro- 

 scopic mount. With a minute description I need not now 

 trouble you, but as neither in Westwood nor in any other of the 

 authorities on juch subjects at my command I can fii d any 

 record of this singular fact havii g been hitherto observed, either 

 in connection with the parasitic Hymenoptera or any other 

 similar insects in the perfect state adapted apparently to an 

 aerial life alone — that they should quit their natural habitat for 

 so lengthened a sojourn in the wa'er — 1 would make the inquiry 

 as to wheiher any like occurrence has been noted by any of your 

 other correspondents. Edwin b'oSTOCK 



Stone, October 6 



[Our correspondent Las had the good fortune to re-discover in 

 this country the little Hymenopterous insect found almost simul- 

 taneously by Sir John Lubbock and Mr. Duchess in 1862, to 

 which the former applied the name Po'yfwma nntaus {Ti ansae- 

 tions of Linnean Society, vol. xxiv. part ii. p. 13S, 1863). The 

 insect is parasitic in its larval stage in the eggs of dragon-flies. 

 A brief summary < f its peculiarities is given in Lubbock's 

 " Origin and Metamorphoses of Insects" (Macmillan and Co., 

 1874). More recently Prof. Westwood has suggested (Transae- 

 ^w?« of Linnean Society, second series, " Zoology," vol. i. part 

 viii. p. 584, 1879) that the insect is scarcely a true Polynenia, 

 but rather an Anaphes, or the type of a new genus. A true 

 Ichneumon (Agriotypns armalus) has long been krown to be 

 parasitic in caddis-worms, and therefore also aquatic in its 

 habits.— Ed.] 



Practical Physics for Boys 



In Prof. Parker's very valuable and interesting paper (vol. xxiv. 

 p. 54) 3 'le says : "The consequences of setting large classes of 

 young boys to make oxygen, or to take a specific gravity . . . 

 each for himself, might prove rather subversive of order than 

 conducive to improvement." It may be inteietting to some of 

 your readers to know that at Clifton College we have lately 

 tried the experiment of turning some of our ordinary physics 

 classes, numbering from twenty-four to thirty b( ys, bodily into 

 the physical laboratf ry, where they work at weighing, measuring, 

 finding specific gravities and such matter's, under the control of a 

 single master. The boysw. rk in pairs, each with a little maiiual 

 of instruction, and each pair with a separate cupboard of cheap 

 apparatus. Two such classes are fallen by Mr. Worthiugton 

 and myself, and we are both agreed that whatever difficulties n-e 

 may feel, we have none in the matter of discipline. On the 

 contrary, the boys are with scarcely an exception most keen and 

 eager at this work. I understand that siradar classes in practical 

 chemistry v\ ill shortly be set on foot by Mr. Shenstone in our 

 chemical laboratory. H. P. Jupr 



Clifton College 



A New Comet 



I OBSERVED a telescopic cnmet in Leo on the mornings of 

 October 4, 5, 6, and 10. The rough positions, as I estimated 

 them, were R.A. gh. 22m., Dec. 16° N. on the 4th, and R.A. 

 9h. 36m., Dec. 15° N. on the loth. The motion is about 30' daily 

 ea^twards. When the present bright moonlight is gore the 

 comet w ill be a fairly bright object in the telescope. At the end 

 of the present week it must be looked for immediately preceding 

 ■q Leonis. 



When I saw it first, on the morning of October 4, it looked 

 like a blight nebula, and I cannot understand how I missed it 

 on the mornings of September 29 and October i, when I had 



carefully swept the same region for several hours before sunrise. 

 The inference is that it is getting brighter. W. F. I'ENMNr; 

 Ashley-Down, Bristol, October 10 



A Kinematical Theorem 



Some little time ago Mr. Kenqie published in Nature a 

 theorem of interest in kinematics. I subsequently stated in the 

 same pages that this theorem avd all theorems of uniplanar 

 kinematics are mcst simply and properly proved from the con- 

 sideration that epicycloidal motion is the basis of all uniplanar 

 motion — and that this is also the proper principle on which to 

 base the theory of planimeters. It may not be out of jilace to 

 occupy a few lines in Nature with another curious kinematical 

 theorem allied to Kempe's, whicli I have just found by this 

 method. If a plane. A, move abcul in atty manner over a fixed 

 plane, K, ami rcltirn to its original position after any number of 

 revolutions, all those right linis in the plane A which have enve- 

 loped glisetles of the same area, are tangents to a eonie, and by 

 varying the area of the glisette we obtain a series of eon fecal conies. 

 I Use the X.drm glisette -ani^t protest — "line roulette" would be 

 better, as the former name is more applicable to a curve of 

 another sort. George M. Minxhin 



Koyal Indian Engineering College 



Integrating Anemometer 

 - My attention wascalltd to a letter on this subject in y.vir issue 

 ofthe 29th ult. (vol. xxiv. p. 510), thoui,h not in time to enable me to 

 answer it lat week. I t.ike this opportunity of stating that the 

 gentleman to whom the idea of the instrument was originally 

 dne, and who has defrayed the whole cost cf its conslruction, is 

 the Rev. j. M. Wilson, M.A., head-master of Clifton College 

 (not Dr. Wilson, as mis-stated in the Association Journal at 

 York and in your ab-tract). The ol jection that the air does not 

 move " parallel to itself," by which 1 presume is meant in planes 

 parallel to its general direction, does not ajply to this any more 

 than to any other cup anemometer. Only the horizontal com- 

 ponent of the wind's velocity is sought, and this is given with 

 tolerable accuracy. I have no means of knowing to what extent 

 Mr. Burton's integrator resembles tlie anemometer in question, 

 but it should be noticed that the two instruments are of a dif- 

 ferent kind and for a different purpose. Mr. R. Scott was in 

 the chair when the paper was read at York, and joined in the 

 discussion. Prof. Stokes was also present, and has since been 

 in correspondence with me on the matter. Neither of these 

 gemlea^en, however, mentioned any other instniment as at all 

 resembling it ; indeed upon its being compared to that of Dr. 

 von Oetlinger, Mr. Scott took occasion to point out at least one 

 important difference, viz. the cost. H. S. Heie Shaw 



University College, Bristol, October 10 



Infusorial Parasites on Stickleback 



Mr. N. H. Poole (Nature, vol. xxiv. p. 4S5) is app.irently 

 right in anticipating that he has discovered either a new habitat 

 for Trichodina fcdiculisox a new representative of that infusorial 

 genus. Althoui/h hitherto regarded as a parasite only of the 

 fresh-water polypes, /iydra vulgaris and //. viridis, I have 

 recently olitained specimens of the type in question living as a 

 parasite, or rather a commensal, on the branchial appendages of 

 the larva of the common newt, Triton cristatus. An allied, but 

 marine species, Trichodina scoipiaia, has been recently descril ed 

 by Prof. Ch. Robin, that infests in a similar manner the branchia 

 of fishes belonging to the genera Trigla and Scorpccna, and a 

 further search will no doubt reveal a yet more extensive distritu- 

 li in of the Urceolari-die, including Trichodina, among the 

 Piscine race. Mr. Poole will find full particulars of the data 

 here referred to, together with an account and illustrations of all 

 the forms so far relegated to this somewhat remarkable infusorial 

 gr up, in Part V., p. 645 tt scq., of my "Manual of the In- 

 fusoria," just published. W. Saville Kent 



The Dark Day in New England 



Referring to your paragraph in last w-eek's Nature (p. 540) 

 about the remarkable phenomenon which occurred in New 

 England on September 6, T find in the recently-published 

 "History of Lynn, Massachusetts," the following : — 



"1716. — Exiraordinary darkness at ncorday October 2 1st ; 

 dinner tables lighted." 



"1780. — Memorable dark day May 19th ; houses lighted as 

 at night." CHARLES \V. HARDING 



Lynn, October 7 



