HA RD WICKE' S SCIENCE- G OS SIP. 



155 



elaborate works, to which, however, I had no access ; 

 and, though I have since borne the matter in mind, I 

 have never met with anything that threw any light on 

 the subject. 



About six weeks since, learning that the Belfast 

 Field I Naturalists, among whom there are several 

 experienced microscopists, were to hold a micro- 

 scopical evening, the thought occurred to me to send 

 to the meeting a figure and brief description of my 

 little animalcule on stilts, in the hope of eliciting 

 some information respecting it ; when I was surprised 

 at being informed by the secretary that none of the 

 members of the club present at the meeting knew 

 anything about it. 



I have on several occasions during the past fourteen 

 years examined water and duckweed from the little 

 stream from which I obtained my interesting speci- 

 mens, but am sorry to say I have not been successful 



in getting more. 



W. S. Smith. 



Manse, Afitrim, Ireland. 



LINES OF ELECTRICAL INDUCTION. 



Ey B. W. Chapman, M.A., B.C.E. (Adelaide 

 University). 



SOME very pretty experiments showing the lines 

 of electrical induction across an insulating 

 medium may be made by using as the insulator pure 

 turpentine besprinkled with the small white needle- 

 like crystals of sulphate of quinine. To perform the 

 experiments, take a flat glass dish, and pour in 

 turpentine to the depth of about a quarter of an inch. 

 The turpentine should be perfectly pure and dry, or 

 it will not act as a non-conductor. Having sprinkled 

 this uniformly with sulphate of quinine, place two 

 brass balls in the vessel, one at either end, and 

 connect them by means of chains, one with an 

 electrical machine, and the other with earth. On 

 •electrifying the machine, the crystals suspended in the 

 turpentine will become polarised, and form in curved 

 lines, end on end, between the metal balls, in 

 exactly the same way as iron filings take up the 

 lines of magnetic induction between the poles of a 

 magnet. 



This experiment may be varied in a great number 

 of ways, by varying the number and shape of the 

 electrified bodies placed in the medium. It may be 

 used to show in a very pretty manner that there is no 

 electric force within a closed conductor. To do this, 

 a metal ring connected with the machine should be 

 placed between the two balls, both of which should 

 be connected with earth. On working the machine, 

 the lines of force will be seen very distinctly mapped 

 out between the balls and the ring ; but within the 

 ring, the quinine is seen to be in the uniformly cloudy 

 state in which it was before the] electrification of the 

 system. The same thing will of course happen if the 



circular ring be replaced by any closed conductor, 

 such as a stout wire triangle or rectangle. Again, if 

 one of the balls be placed in the centre of a large 

 metal ring, the ball connected with the machine, and 

 the ring with earth, or vice versa, the lines of force 

 become radial straight lines from the centre to the 

 circumference of the ring, and are mapped out with 

 perfect clearness by the quinine crystals. The lines 

 of induction may be rendered very complex by having 

 a larger number of balls in the vessel, some attached 

 to the machine, and others to earth, but they are in 

 all cases distinctly marked by the crystals. By 

 placing the glass dish upon an ebonite plate, thus 

 securing a dark background, I have been enabled to 

 secure photographs of a number of interesting cases. 



THE CANNIBALISM OF THE LADYBIRD 

 (Coccinella dispar). 



WHETHER the pupse of this useful insect are 

 protected by their peculiar odour against 

 other enemies, it is not decided. But they are sadly 

 open to the attacks of the larva; of their own 

 species. It must be confessed that C. dispar, with 

 probably its congeners also, is a cannibal. When a 

 larva in its travels encounters a pupa, moored by the 

 posterior extremity to a leaf and unable either to fight 

 or flee, it at once seizes the booty from behind. I 

 have watched not a few such encounters through a 

 lens, and have distinctly seen the mandibles of the 

 larva plunged into the body.of its victim, and working 

 very diligently. The pupa which is thus being 

 devoured at times raises its head or moves it from 

 side to side, until its life is extinct. Mr. Billups, 

 F.E.C., one of our most observant entomologists, tells 

 me that he has observed similar cases. But as his 

 cannibal specimens were in captivity, he suspected 

 that they might have been driven to such an un- 

 natural diet from want of their legitimate prey, 

 aphides, I am sorry that I cannot give the ladybirds 

 the benefit of this doubt. I witnessed instances of 

 cannibalism, not merely in a glass box in which I 

 had placed some larvae and pupae, but on a row of 

 black-currant bushes where aphides were swarming. 

 Hence, I fear that the Coccinellse are deliberate 

 and habitual cannibals. It is needless to ask if this 

 practice must not seriously interfere with the multi- 

 plication of the species, and limit its usefulness as 

 an aphis destroyer. 



Whether this form of cannibalism tends to weed 

 out the strongest or the weakest members of the 

 species, I am not able to determine. The destruction 

 falls chiefly upon the progeny of such ladybirds in 

 each brood as are the earliest to deposit their eggs. 

 If such eggs, as I suspect, give rise to the finest 

 specimens, we have here a process likely to result in 

 the survival of the unfittest. 



I have never seen an adult Coccinella thus attacking 



