March 28, 1895 J 



NATURE 



511 



arranged that when the bob is swinging, and in the position of 

 maximum amplitude nearest the lens, the shadow o( a portion 

 of the wire immediately above the bob, thrown on a screen 

 some 32 feet distant, is clear and distinct, and coincides with a 

 vertical Mack line thrown on the white screen. 



The bob is drawn back towards the lamp about eight inches, 

 by a loop of thread, and when we wish to experiment the 

 thread is then burned in the usual manner. 



When the pendulum completes its first oscillation, the shadow 

 falls exactly on the black line traced on the screen. In about 

 five minutes the shadow has moved to the left of the line, and 

 in ten minutes conspicuously so. In this time the maximum 

 amplitude has decreased so little that the image on the screen 

 is still distinct and clear when the pendulum is in a position 

 nearest the lens. W. R. Westropp Roberts. 



Trinity College, Dublin. 



Snake Cannibalism. 



HAVE read with interest the numerous accounts of snake 



cannibalism which have lately appeared in Nature. During 



n^y residence in South Africa, I have come across several in- 



ilances of a similar nature. A few weeks ago I received a large 



loughals {Sefcdon luemachate) which had swallowed another 



cne of the same kind and of nearly its own length. As the sw.-il- 



lowed individual was too long to disappear completely before 



the front portion of its body was digested, its tail was sticking 



cut of the mouth of the swallower by about six inches. I have 



cissected two )ellow coVras (Naja haji), each of which had 



swallowed a puff adder ( F//«rtar7V/a>M) more I ban three feet long. 



This case is very interesting, as the puff adder has much larger 



fargs Ihsn the yellow cobra, and in a fight the latter would 



piobably succumb. To mention only one more case, I received, 



:ome yeais ago, the skins of a cross-marked schaapsticker 



[r.aninu'/his ouci/cr) and a spotted schaapsticker (/"Mmmc- 



jltylax rhombiatiis), the former of which had swallowed the 



latter. In all cases which have come under my personal obser- 



^aticn ihe swallowed snakes had entered head first, and thus 



] lobably they wtre simply drawn in after having caught hold 



o( the same piey as the swallowers. In conclusion, I may men- 



licn that cases similar to the above are frequently described in 



'.he South African newspapers. J. SCHONLAND. 



Grahamstown, South Africa, March i. 



American Frtsh water Sponges in Ireland. 



A SHORT lime ago, Dr. R. F. Scharff, Dublin, sent me a 

 .-mall colUclicn of Iri'h Spongillidae. The examination of the 

 nratciial resulted in the discovery of two or three American 

 species, obtained from the West of Ireland, viz. Hetercmeyctiia 

 lyJcti, Polts, lubella fcntnylvanita. Potts, and (?) Ephydaiia 

 aataijc) »n's, Polls, ihe fiisl of these three species having been 

 identified by Dr. W. Wcllner, Berlin. All these species are 

 r.ew 10 Euicpe, and as they were found in a small collection 

 taken mere cr less at rar.dcm, it is probable that if the fresh- 

 water fauna of ihe West of Ireland were thoroughly investi- 

 gated, a great many moie American species would be dis- 

 covered. 



Details will be published in the May number of the Irish 

 Naliiralist. R. Hanitsch. 



University College, Liverpool, March 13. 



Peripatus in the West Indian Islands. 



■West Indian records show that occasionally single speci- 

 mens of ^arious species of I'eripalus have been found in the 

 different islands. During the past week, Mr. Lunt, my 

 assistant, found a single specimen, and a further search being 

 organised, lesulled in the capture, by two collectors, of fifty 

 specimens. These, it is believed, belong to two different 

 species, and a goodly number of the specimens have been sent 

 for determination to the liritish Museum. 



Either the animals are more numerous than usual, or the 

 previous search for ihem has not been a very careful one, as 

 the whole of our specimens were found within the precincts of 

 the Gardens. J. II. Hart. 



Royal Botanic Gardens, Trinidad, March 6. 



NO. 1326, VOL. 51] 



Planetary Photography. 



I understand that in photographing a planet, such as Mars, 

 only a short exposure can be allowed, because there is no way 

 of compensating the planet's a.na/ rotation. But, while follow- 

 ing the planet with the equatorial, would it not be possible to 

 compensate this axial movement by slowly sliding the plate, so 

 that certain features of the planet should fall always on the 

 same parts of the plate? If this is so, an exposure of some 

 lenglh might be available for the more central portions of the 

 disc, those portions for which, during the interval, no serious 

 alteration due to foreshortening comes into play. 



Cardiff, March 23. C. T. Whitmell. 



Cleaning Tobacco Pipes. 



I HAVE discovered a new method for cleaning pipes which 

 have become foul. A shallow cork, through which a hole is 

 bored large enough to enable it to fit tightly on to the nozzle 

 of a soda-water syphon, i; fitted into the bowl. The nozzle is 

 inserted, the mouth-piece directed into a vessel, about a wine- 

 glassful of soda-water forced through, and the pipe is clean 1 



This is not a scientific discovery, but it may be of use to 

 those scientific men who are smokers. Rubber stoppers answer 

 better than corks. Cecil Carus-Wii.son. 



THE HABITS OF LI Af PETS. 



SOME observations made by the present writer at the 

 Scottish Marine Station during July 18S4, were 

 published in N.vruKf: for January i, 1885. These obser- 

 vations confirmed the statements previously made by 

 various naturalists, from Aristotle onwards, that the com- 

 mon limpet (Patella vuli^ata) settles down on some 

 eligible spot (its " scar") between tide-marks, and makes 

 a home, to which it returns after havinfr been out to 

 feed. The conclusion was drawn from various data that 

 this " locality sense " is independent of smell, sight, 

 and touch so far as the head-tentacles are con- 

 cerned. Prof Lloyd Morgan, in a letter to Nature 

 (" Homing of Limpets," December 6, 1S94), has shown 

 that the limpet possesses an even greater power of 

 " homing'" than previous observers have suspected, and 

 he believes that the head-tentacles are the sense-organs 

 concerned. 



Since 1S84, I have made further notes, and aided by a 

 grant from the Research Grants Committee of the Royal 

 Society, to whom my best thanks are due, have pursued 

 the subject with some care during the past year. The 

 results, apart from those connected with histology, here 

 follow. 



The limpets observed live on a reef, which extends 

 several hundred yards seaw^ards (practically west) from 

 the front of Aberystwvth College. The rocks are 

 Silurian grits and imperfect slates, alternating in a very- 

 regular way, striking north and south, and tilted at high 

 angles. At low tide the Lamittaria zone is well exposed, 

 and for some yards above this the rocks are somewhat 

 bare, except that they are thickly encrusted with small 

 halaiii. Nearer the land various brown seaweeds 

 (mostly Fiicus scrratus. F. vcsiculosus, and Ozothallia 

 nodosa) thickly cover the reef, except towards high-water- 

 mark, where they become scanty. Throughout this area 

 limpets of all sizes abound, being specially numerous, 

 however, on the barnacle-encrusted rocks above men- 

 tioned. Groups of them were here marked with enamel 

 paint, and watched. A number of observations were 

 also made on the small limpet, which lives on Laiiunaria, 

 and has its shell marked by three diverging blue streaks 

 {Ih'ldon pellucidiim = Patella pellucida). 



Food and Feeding. — As before, the chief food noticed 

 consisted of the minute alga- coating the halani and 

 rock-surfaces. Specimens were also found feeding on 

 the calcareous seaweeds Corallina and Melol'csia, on 

 Fi/ctis, and on Laminaria. It was suggested in Ihe pre- 

 vious notes that the great length of the radula is perhaps 



