146 



NATURE 



\ynne i-j, 1880 



it may not be generally known that more than thirty years ago a 

 skating pond «as constructed in Liverpool, consisting, I believe, 

 entirely of crystallised Glauber's salt. I have a perfect recollec- 

 tion of this miniature lake wiih its grotto-like surroundings, of 

 its black looking ice with innumerable white scorings marking 

 the tracks of the skaters, yet, strange to say, I cannot remember 

 whether I skated on it myself. The impression that I did seems 

 to be confused w ith other skating scene?. This perhaps does 

 not look like very reliable evidence, but that the " riiik " (under 

 another name) of artificial ice did exist, and was popular, will no 

 doubt be affirmed by many witnesses besides myself. The date 

 would be about 1845, if I am not mistaken, and the speculation 

 ultimately failed owing to a public impression (possibly a wrong 

 one) that the exhalations from the surface of the poud caused 

 sickness and headache. R. H. 



The Stone in the Swallow 



Your correspondent, Dr. P. P. C. Hoek, requests informa- 

 tion respecting the origin of the fable to which the poet Long- 

 fellow refers at the end of the first part of " Evangeline " — 

 " The stone in the nest of the swallow." In Burton's "Anatomy 

 of Melancholy," p. 434, at the top (\Vm. Tegg's edition), after 

 describing in the delightfully quaint style of the age the curative 

 virtues of various stones, he quotes the following: — 



" In the belly of a swallow there i- a stone called 'chekdo- 

 nius,' ^^■hich, if it be lapped in a fair cloth and tied to the right 

 arm, will cure lunatics, madmen, make them amiable and 

 merry." 



In a foot-note there are references made to the following 

 authors : — Albertus, Eucellius, cap. 44, lib. 3 ; Plin, lib. 37, 

 cap. 10 ; Jacobus de Dondis, &c. 



It seems probable that Longfellow got his version of the story 

 from some of the descendants of the French Acadians, to whom 

 the poem relates, and it may have come down from the same sources 

 from which Burton derives his account of the matter. It may 

 be noted that the two versions do not in any way clash. Burton's 

 simply referring to the whereabouts of the stone, "in the belly 

 of the swallow," its name and benefits to those afflicted wiih 

 insanity; while Longfellow's version relates more to the finding 

 and locality of the stone and its uses to the young swallows, 

 leaving its supposed value to man, depending on the general 

 term of being "lucky." John Locke 



Trinidad, West Indies, May 24 



Stags' Horns 



In reference to the opinions recently expressed in your journal 

 regarding the disappearance of the horns of stags, deer, &c., 

 1 may mention that this is usually attributed here to the action 

 of rodents rather than of the deer themselves. Even if a deer 

 should occasionally be seen gnawing a horn it would be very 

 difficult to account for the disappeara-ce of all the annual crop 

 of antlers in this way. From the nature of their dentition (having 

 no incisor teeth in the upper jaw) the destruction of such a mass 

 of hard material must be very difficult. Moreover slight examina- 

 tion will show whether the tooth marks are those of the large 

 teeth of a deer or of the small incisors of a rodent. 



Antioch College, Ohio, U.S.A. E. W. CLAYrOLE 



ON SOME POINTS CONNECTED WITH 

 TERRESTRIAL MAGNETISM 



T HAVE on more than one previous ocsasion brought 

 ^ forward some of the various points which arc here 

 grouped together. These points are three in number. 



(a) Regarding the sustaining power of the earth's 

 magnetism. 



(/3) Regarding the diurnal and other changes of the 

 same. 



(y) Regarding earth currents and auroras. 



I may state at once that this only professes to be a 

 working hypothesis. 



(a) RcgardiUi^ the Sustniiung Power of the Earth's 

 Mas^netisin. — I do not here intend to discuss the cause of 

 the earth's magnetism, but I would ask in the first place if 

 it is not possible that this cause may be something small 

 and one which (assuming it to continue at the present 



moment) we may not readily perceive. If we assume this 

 cause or magnetic nucleus to be small is it not possible to 

 im.agine that there is a machinery which acts upon this 

 nucleus (just as we have in certain magneto-electric 

 engines) so as to swell up the magnetism of the earth 

 ultimately to saturation.' 



May not this machinery be the great convection 

 currents, the anti-trades, that go from the equator to the 

 poles in the upper regions of the earth's atmosphere, and 

 which may be looked on as conductors moving across 

 lines of magnetic force ? 



It would appear to me that the tendency of such cur- 

 rents will be to swell up and sustain the magnetism of the 

 earth. 



O) Reoarding the Dizcynal and other Changes of 

 Terrestrial Magnetism. — It will of course be natural, 

 entertaining the views now enunciated, to regard the 

 diurnal changes of the convection currents of the earth's 

 atmosphere, as these are tnanifested in the upper regions, 

 to be the cause of the diurnal changes of terrestrial 

 magnetism. 



If this view be taken it might be argued that wind 

 changes in these upper regions should also produce mag- 

 netic variations. The reply is that apparently they do. 

 In conjunction with Mr. Morisabro Hiraoka I have com- 

 pared together the simultaneous records of magnetic 

 declination ranges at Kew and at Trevandrum, and I 

 find evidence of a progress of things from west to east, 

 so that on the whole a particular magnetic-range phe- 

 nomenon occurs at Kew 97 days before it occurs at 

 Trevandrum. Again, I have attempted to show, in con- 

 junction with Mr. Dodgson, that a particular magnetic 

 phenomenon occurs at Kew one day before it occurs at 

 Prague. 



It would thus appear that there is a progress of mag- 

 netic phenomena from west to east, just as we know there 

 is a progress of meteorological phenomena. As, however, 

 the meteorological phenomena which we can examine 

 occur in the io'cuer atmospheric regions, while the mag- 

 netic phenomena are, according to this hypothesis, asso- 

 ciated with currents in the hig/ier regions, it does not 

 follow that magnetic and meteorological phenomena 

 should travel from west to east at the same rate. I may 

 also mention that we have reason to believe that magnetic 

 changes lag behind corresponding solar changes just as 

 meteorological changes would do. 



It is manifest that it will be comparatively easy to settle 

 the fact of a progress from west to east of magnetic 

 weather, and that if such exists it will most readily ally 

 itself with the hypothesis above mentioned. 



In the ne.xt place, if we regard those changes in the 

 convection-currents of the earth which depend on the year 

 we have reason to imagine that such are most pronounced 

 at the equinoxes. It is also well known that magnetic 

 disturbances are most frequent at these times. 



Let us next proceed to regard the secular change of the 

 earth's magnetism. To account for this magncticians 

 have felt the need of something movable, and the hypo- 

 thesis of a "little earth," a solid nucleus moving within 

 the recesses of our planet, has found much support. But 

 is it not more likely that the result may be caused by a 

 secular variation in the distribution of the convection- 

 currents of the earth .' If the question be asked. What 

 reason have we for imagining the existence of such a 

 variation, the answer will be, A much better reason than 

 we have for entertaining the conception of a "little 

 earth." For there is some reason, at any rate, for imagin- 

 ing the power of the sun to be subject to a complicated 

 series of per'ndicities. Now a secular variation in the 

 po.ver of the sun would produce a secular change not only 

 in the intensity, but in the direction of the convection- 

 currents of the earth, and, according to the above hypo- 



If I .im not mistaken Sir W. Thon 

 lagneto-electric engine. 



iclinej to regard the earth as 



