Dec. I, 1887] 



NATURE 



105 



sands of that division. To whatever division, however, of the 

 Hagshots these beds may be assigned eventvially, the occurrence 

 of fossils in them is, I think, worthy of record. 



53 Warwick Square, November 25. R. S. Herries. 



The Ffynnon Beuno and Cae Gwyn Caves. 



Since writing my note, as published in Nature of Novem- 

 ber 3, p. 7, I have paid another vi^it to the British Museum, 

 and seen a second implement from the Denbighshire caves, 

 presented by Dr. Hicks and Mr. Luxmore. It is a small 

 and highly-finished scraper, exactly agreeing with the Neolithic 

 scrapers of Icklmgham and Mildenhall, and with small scrapers 

 found in caves of confessedly very late da'e. This scraper is 

 quite sufficient to condemn any pre-Glacial theory, and it en- 

 ables me to emphasize my former remark that the cave contents, 

 instead of belonging to the earliest Palaeolithic class, belong to 

 the very litest. I do not believe that a similar scraper has ever 

 been found in any really old, or even moderately old, Pahrolithic 

 river gravel. Such scrapers were only made in the most recent 

 of Palaeolithic times. 



Mr. G. H. Morton is not justified in his remark (Nov. 10, p. 32) 

 that my former letter afforded " a remarkable instance of rushing 

 into print and giving ai opinion on a subject with which the 

 writer was unacquainted," for I have studied the drifts of Wales 

 for twenty years, and during that time I have never failed to make 

 one or two visits a year to Wales. I have also examined nearly 

 every cave in North and South Wales, and handled the shovel 

 and pickaxe myself. From the experience I have obtained 

 during this time, I say the drift in front of the Denbighshire 

 caves is not in its oris^inal position, but distinctly and obviously 

 relaid ; and I even doubt whether before it was relaid it was 

 a true Glacial gravel at all. 



I will "read up the literature of the subject" if I get time : 

 in the meantime there is no great harm done in expressing an 

 opinion from a study of some of the real objects, even if that 

 opinion is " not worth anything" and "of no consequence," as 

 Mr. Morton concludes. WorthIxN'GTON G. Smith. 



Meteor. 



On Tuesday night, November 15, a wonderfully fine meteor 

 was seen at Falmouth, and being out star-gazing at the time, I was 

 fortunate enough to see it. I was looking towards that part of 

 the Milky Way between Auriga, Perseus, and Cassiopeia, when 

 suddenly a curved train of light flashed out ; but, instead of just 

 going away, it remained visible for quite eight seconds ; mean- 

 while the lower extremity burst into a brilliant mauve "cone" of 

 light, about a quarter the size of the full moon. So bright was 

 it that it lit up the roadway, quite overpowering the lamps. 



It was a grand sight, and I sincerely hope other eyes than 

 mine saw it. B. Truscott. 



4 Alma Crescent, Falmouth. 



MODERN VIEWS OF ELECTRICITY.^ 

 Part III. — Magnetism. 



V. 



"\17'E next proceed to consider electricity in a state of 

 ** rotation. What happens if we make a whirlpool 

 of electricity 1 Coil up a wire conveying a current, and 

 try. The result is it behaves like a magnet : compass- 

 needles near it are affected, steel put near it gets mag- 

 netized, and iron nails or filings get attracted by it — 

 sucked up into it if the current be strong enough. In 

 short, it is a magnet. Not of course a permanent one, 

 but a tempora'-y one, lasting as long as the current flows. 

 It is thus suggested that magnetism may perhaps be 

 simply electricity in rotation. Let us work out this idea 

 more fully. 



First of all, one may notice that everything that can 

 be done with a permanent magnet can be imitated by 

 a coiled wire conveying a current. (It would not do 

 altogether to make the converse statement.) Float a coil 



' This Part is an expansion of a lecture delivered at the London Institution 

 on January 5, 1885. Continued from p. 13. 



attached to a battery vertically on water, and you have a 

 compass-needle : it sets itself with its axis north and 

 south. Suspend two coils, and they will attract or repel 

 or turn each other round just like two magnets. 



As long as one only considers the action of a coil at 

 some distance from itself, there is no need to trouble 

 about the shape of the particular magnet which it most 

 closely simulates ; but as soon as one begins to consider 

 the action of a coil on things close to it, it is necessary to 

 specify the shape of the corresponding magnet. 



If the coil be a long cylindrical helix like a close-spired 

 corkscrew, as in Fig. 16, it behaves like a cylindrical 

 magnet filling the same space. But if the coil be a short 

 wide hank, like a curtain-ring, it behaves again like a 

 cylindrical magnet, but one so short that it is more easily 

 thought of as a disk. A disk or plate of steel magnetized 

 with one face all north and the other face all south can 

 be cut to imitate any thin hank of wire conveying a 

 current. It will be round if the coil be round, square if 

 it be square, and irregular in outline if the coil be 

 irregular. 



There is no need for the coil to have a great number of 

 turns of wire except to increase its power : one is suf- 

 ficient, and it may be of any shape or size. So when we 

 come to remember that every current of electricity must 

 necessarily flow in a closed circuit, one perceives that 

 every current of electricity is virtually a coil of more or 



Fig. 16. — Floating b.ittery and helix acting as a coTipass-needle. 



less fantastic shape, and accordingly imitates some magnet 

 or other which can be specified. Thus we learn that 

 every current of electricity must exhibit magnetic phe- 

 nomena : the two are inseparable — a very 1 important 

 truth. 



There is one detail in which the magnetized [disk and 

 the coil are not equivalent, and the advantage lies on the 

 side of the coil : it has a property beyond that possessed 

 by any ordinary magnet. It has a penetrable interior, 

 which the magnet has not. For space outside both, they 

 simulate each other exactly ; for space inside either, they 

 behave differently. The coil can be made to do all that 

 the magnet can do ; but the magnet cannot in every 

 respect imitate and replace the coil : else would perpetual 

 motion be an every-day occurrence. 



Now I want to illustrate and bring home forcibly the 

 fact that there is something rotatory about magnetism — 

 something in its nature which makes rotation an easy 

 and natural effect to obtain if one goes about it properly. 

 One will not observe this by taking two magnets : one 

 will see it better by taking a current and a magnet, and 

 studying their mutual action. 



A magnet involves, as you know, two poles — a north 

 and a south pole— of precisely opposite properties : it 

 may be considered as composed of these two poles for 

 many purposes ; and the action of a current on a magnet 

 may be discussed as compounded of its action on each 

 pole separately. Now how does a current act on a 

 magnetic pole t Two currents attract or repel each 

 other ; two poles attract or repel each other ; but a 

 current and a pole exert a mutual force which is neither 

 attraction nor repulsion : it is a rotatory force. They tend 

 neither to approach nor to recede ; they tend to revolve 



