278 



KNOWLI'.IX'.I-: 



jLi.v, 1912. 



AL'TOCHROMIC SCRKHN. — From Messrs. J. II. 

 Dallineyer, Ltd., of 2.S, Newman Street, Oxford Street, we 

 have received ati Autocliroiiie screen in optical Hats suitable 

 for use with hi^li-class anasti|i;iiiats, telcphoto, process and 

 other lenses. Tlicse screens are made in diameters varying' 

 from one and a li.ilf inches to three inches ,and at prices from 

 twenty-two shillinj;s to fifty shillinKs. They are worked to an 

 accuracy of a one-five-hundrcd-thousandth part of an inch. 



We have examined this screen and consider that it fully 

 bears out the claim made for it by the makers, and the high 

 r<-putation enjoyed by Messrs. Dallmeyer should be sufhcient 

 guarantee of its excellence. 



I'llWSICS. 



Hy .\i.i-RiiD C. G. Egerton, H.Sc. 



SKMIOILV LIQUIDS ON A WATLK SURFACE.— 

 When a drop of li(juid is placed on a water surface the effect 

 produced depends on the solubility of the licjuid. An oil 

 forms a permanent film ; but a sliylitly soluble li(|uid forms a 

 film which breaks up into globules. The globules are formed 

 by indentations spreading rapidly into the films and causing 

 partition. Sometimes the globules are projected violently 

 across the surface of the water. Mr. C. R. Darling has made 

 a careful study of these effects which he has brought to the 

 notice of physicists : his last paper to the Physical Society on 

 the subject was read on Friday. May 1st. He has investi- 

 gated many organic liquids, among the most interesting 

 being aniline, dimethylanilinc, quinoline, and 1:3:4 xylidine. 

 Aniline, after spreading into a film, collects into one or more 

 large globules, which become indented round the edges and 

 then recover their shape with partition of a few small 

 globules. Dimethylanilinc breaks up into small globules 

 uuich more rapidly ; the indentations spread and bifurcate 

 very rapidly, dividing the film into globular portions. 



Quinoline behaves very much like dimethylauiline, but 

 works slower. The small globules formed in this case finally 

 become rings which arc quite permanent and distinctive of 

 quinoline. 



Xylidine and orthotoluidiue form globules which become 

 indented on one side and move rapidly across the surface 

 usually away from the side where the indentation has 

 occurred ; the globules become reniform in shape. The 

 globules thus gradually break up into smaller globules. 



Mr. Darling's explanation of these interesting effects is the 

 following : — The surface tension of the water is weakened by 

 the solution of the liquid. The opposing tensions then 

 overcome that of the water, with the result that the film is 

 drawn back and indented. The strength of the air-water 

 tension is then partially restored by the sinking or diffusing 

 of the dissolved part so that the drawn-up mass again tends 

 to spread. Indentations would therefore occur where the 

 air-water tension had become most weakened ; and if the 

 opposing tensions were strong enough, the globule would 

 be drawn across the surface of the water. Ecjuilibrium 

 would be established when the air- water tension had become 

 uniformly weakened and the opposing tensions possessed a 

 resultant tension equal to that of the soiled water. 



It would be interesting to investigate the effects of films of 

 liquids on solvents such as acetone, alcohol, and so on, instead 

 of water ; perhaps similar interesting phenomena would be 

 obtained. 



ZOOLOGY. 



By Proi-essor J. Arthur Thomson, M.A. 



EGG-TOOTH OF BIRDS.— One is glad to hear something 

 more in regard to the so-called egg-tooth of young birds, 

 which is none the less interesting that it has nothing to do 

 with teeth, being simply a horny knob. If it is of use in break- 

 ing through the egg-shell, which seems in some cases at least 

 very doubtful, it is used only once. As everyone knows, it 



soon falls off. The fact suggests the question whether it may 

 not be a derivative of some older structure with a different 

 use ; for this is a common thing in organic evolution, that 

 the apparently new should arise from the very old. Some 

 recent observations by B. Rosenst.idt suggest that the egg- 

 tooth of the upper jaw, and its corresponding vestige on the 

 lower jaw, may be a relic of an ancient armature, older than the 

 horny sheaths we are familiar with. In the first place, the 

 egg-tooth above and the vestige below become horny before 

 there is any other cornification on the jaws. In the second 

 place, the process of making horn in the egg-tooth is different 

 from that elsewhere. Each of the skin cells concerned turns 

 wholly into horn-fibres, nucleus and all, whereas in ordinary 

 cases, as in the horny covering of the jaws, only the mantle of 

 each cell is turned into horn. 



LOCOMOTION IN SNAILS.— When we watch a snail 

 creeping on a pane of glass we see beautiful waves of con- 

 traction passing along- the " sole of the foot," i.e., the snail's 

 nmscular ventral surface. The foot works partly as a holdfast, 

 adhering by its mucous secretion, or by acting like a sucker, or 

 by both means. Professor G. H. Parker has studied numerous 

 Gastropods and finds that the locomotion may be accom- 

 plished without (arhythmic) or with (rhythmic) the pedal waves. 

 Ill rhythmic locomotion the waves may run from posterior to 

 anterior (direct) or the reverse (retrograde), but a snail never 

 moves backwards. The foot may show one, two, or four 

 series of waves. When there are two series, the waves may 

 be alternate or opposite. 



" The pedal wave is an area of the foot that is lifted off the 

 substrate as compared with the rest of the foot and thereby 

 freed more or less from adhesion. It is also the region of 

 the foot that moves forward, the rest of the foot remaining 

 temporarily stationary. Locomotion is the cmnulative result 

 of local forward movement on the part of one section of the 

 foot after another till the whole foot has been moved. The 

 same type of muscular movement as that seen in rhythmic 

 locomotion can be present in a difiuse form (not wave-like) in 

 a gastropod foot and will result in locomotion." 



EFFECT OF ALCOHOL ON GENERATIONS OF 

 ROTIFERS.— Dr. D. D. Whitney studied four strains of 

 parthenogenetic rotifers, originally descended from one female, 

 for twenty-eight successive generations. One strain was 

 kept as a control, the other three strains were kept in a 

 quarter per cent., a half per cent., and one per cent, solution 

 of alcohol. The rate of reproduction was lessened in the 

 alcoholic strains. Those of the one per cent, alcoholic strain 

 showed in the XI-W generations a decidedly increased 

 susceptibility to copper sulphate used as a test of resistance. 

 When the alcohol was removed in generations XI-XXII, the 

 rate of reproduction increased noticeably in the first genera- 

 tion, and in the second equalled that of the control. Indi- 

 viduals of the second generation after the alcohol had been 

 removed were no more susceptible to copper sulphate than 

 those which had never been alcoholised. The general con- 

 clusion is that the grand-children possess none of the defects 

 caused by alcohol in the grand- parents. .Mcohol in the per- 

 centages used art'ects only the body tissues. If the animals 

 were subjected to it indefinitely, generation after generation, 

 the race would probably become extinct because of its 

 " lowered resistance power " to unfavourable conditions. 

 " However, if the alcohol is removed it is possible tor 

 the race to recover .and to regain its normal condition in two 

 generations, thus showing that the germ substance is not 

 permanently affected by the alcohol. " 



MEDUSOll) OF MICKOHVDR.A.— One of the simplest 

 of the freshwater polyps, which have doubtless evolved from a 

 marine stock, is Microhytlni ryilcri Potts, reported some years 

 ago from North .\mcrica. It was known to liberate a minute 

 Medusoid. In 1909, Professor Goette, of Strassburg. recorded 

 its occurrence in (Germany, In the warm summer of last year 

 its medusoid stage —which has been carefully searched for — 

 was found bv W. Schorn, in Finow Canal, near Eberswald. 



