August i8, 1881] 



NATURE 



361 



corresponding to diamagnetism. If, on the other hand, 

 we hang in the water a bull which is heavier than water, 

 its oscillations are not so great as that of the .water in its 

 vicinity, owing to its mass, and consequently the oscilla- 

 tions of the ball relatively to the water are in the opposite 

 direction to those of the water itself, and there is attrac- 

 tion, corresponding to paramagnetism. A rod of cork 

 and another of metal are suspended horizontally by 

 threads in the trough. A vibrating drum is brought near 

 to them ; the cork rod sets itself equatorially, and the 

 metal rod axially. 



If a pellet of iron be floated by a cork on water and two 

 similar poles {e.g. both north) be brought to its vicinity, 

 one above and the other below the pellet, the latter cannot 

 remain exactly in the centre, but will be repelled to a 

 certain distance, beyond which however there is the usual 

 attraction. The reason is that when the pellet is nearly 

 in the line joining the two poles the north pole of the 

 pellet (according to our supposition) is further from this 

 line than the south one. The angle of action is less ; so 

 that although the north pole is further away, the horizontal 

 component of the north pole repulsion may be greater 

 than that of the south pole attraction. Dr. Bjerknes re- 

 produces this experiment by causing two drimis to pulsate 

 in concord, the one above the other. A pellet fixed to a 

 wire, which is attached by threads to two pieces of cork, 

 is brought between the drums, and it is found impossible 

 to cause it to remain in the centre. 



Dr. Bjerknes conceived further the beautiful idea of 

 tracing out the conditions of the vibrations of the water 

 when acted on by pulsating drums. For this purpose he 

 mounted a sphere or cylinder on a thin spring and fixed 

 a fine paint-brush to the top of it. This is put into the 

 water. The vibrations are in most cases so small that 

 they could not be detected, but by regulating the pulsa- 

 tions so as to be isochronous with the vibrations of the 

 spring, a powerful vibration can be set up. When this is 

 done a glass plate mounted on four springs is lowered so 

 as to touch the paint-brush, and the direction of a hydro- 

 dynamic line of force is depicted. Thus the whole field 

 is explored and different diagrams are obtained according 

 to the nature of the pulsations. Using two drums pul- 

 sating concordamly, vre get a figure exactly like that 

 produced by iron filings in a field of two similar magnetic 

 poles. If the pulsations are discordant it is like the 

 figure with two dissimilar poles. Three pulsating drums 

 give a figure identical with that produced by three mag- 

 netic poles. The professor had previously calculated 

 that the effects ought to be identical, and I think the 

 same might have been gathered from the formula; in Sir 

 William Thomson's " Mathematical Theory of Mag- 

 netism," but this only enhances the beauty of the experi- 

 mental confirmation. 



Physicists have been in the habit of looking upon 

 magnetism as some kind of molecular rotation. Accord- 

 ing to the present view it is a rectilinear motion. Physi- 

 cists have been accustomed to look upon the conception 

 of an isolated magnetic pole as an impossibility, but here, 

 while the oscillating sphere represents a magnetic mole- 

 cule with north and south poles, the pulsating drum 

 represents an isolated pole. These are new conceptions 

 to the physicist, let us see whither they lead us. The 

 professor shows that if a rectilinear oscillation constitutes 

 magnetism, a circular oscillation must signify an electric 

 current, the axis of oscillation being the direction of the 

 current. According to this view what would be the action 

 of a ring through which a current is passing? If the 

 ring were horizontal the inner parts of the ri g would all 

 rise together and all fall together, they would vibrate and 

 produce the same effect as the rectilinear vibrations of a 

 magnet. This is the analogue of the Araperian currents. 



To illustrate the condition of the magnetic field in the 

 neighbourhood of electric currents, Dr. Bjerknes mounted 

 two wooden cylinders on vertical a.xes, connecting them 



by link-work, which enabled him to vibrate them in the 

 same or opposite ways. To produce enough friction he 

 was forced to employ syrup in place ot water. The 

 figures which are produced on the glass plate are in every 

 case the same as those which are produced by iron filings 

 in the neighbourhood of electric currents, including the 

 case of currents going in parallel and in opposite direc- 

 tions. 



The theory is carried out a step further to explain the 

 attraction and subsequent repulsion after contact of an 

 electrified and a neutral substance and the passage of a 

 spark. But it is extremely speculative, and is not as yet 

 experimentally illustrated, and I think that at present it 

 is better to pass it by. 



I believe that the professor will exhibit his experiments 

 and give some account of his mathematical investigations, 

 which have occupied his time for five years, to the Aca- 

 demic des Sciences this afternoon. His results have not 

 been published before. George Forbes 



Paris, August 15 



NOTES 

 John Duncan, the Alford. weaver-botanist, has at last 

 parsed away, and his dust now lies under the earth whose 

 beautiful childrea he knew aud loved so well. He expired a 

 little after noon on the gth iustant, in his eighty-seventh year, 

 and was buried on the l6th in the old churchyard at Alford, in 

 a selected spot, where a monumeut will soon be raised to his 

 memory by the free-will offerings of those who admired liis high 

 chaiacter and pure-minded enthusiasm for science. The poor 

 old man has not lived long to enjoy the comforts lately provided 

 for him, but it is pleasant to tliink that this aged and unselfish 

 student of nature passed the last days of his long and silent life 

 in comparative affluence, and that he now rests in no pauper's 

 grave. His life was so recently sketched in these pages (Nature, 

 vol. xxiii. p. 269) that it is unnecessary here again to rehearse it. 

 In December last, when it was ascertained that, after an un- 

 usually laborious life, winning his daily bread by weaving, 

 carried on till beyond his eighty-fifth year, he had through failing 

 strength been at last reluctantly forced to fall on the parish for 

 bare support, an appeal was made in his favour by Mr. Jolly, 

 H.M. Inspector of Schools, in the newspaper press throughout 

 the country, and in our own columns. The response was speedy 

 and ample, so that in a very short lime a sum of 326/. was 

 spontaneously sent for his relief, with every expression of ad- 

 miration and regret from all parts of the land, aud from most of 

 our most eminent scientific men, whose kindly appreciation of 

 his scientific labours was not unfrequently very aptly and 

 memorably put. His pride and appreciation of all this kind- 

 ness were genuine, deep, and child-like, and were expressed 

 not seldom in piquant and touching terms; so that his 

 ntimerons friends have the great satisfaction of thinking, 

 that by their means, though he has depai-ted sooner than 

 was anticipated, they have helped to comfort the evening of 

 his days. His constitution was of the healthiest type, and his 

 tenacity of life remarkable in a frame so exhausted, and he only 

 passed away when the last particle of the expiring taper was 

 slowly consumed. As already told in Nature (vol. xxiv. p. 

 6), the money raised in John Duncan's behoof has been vested 

 in seven trustees, under a trust-deed executed during his life. 

 By its provisions his valuable books on botany and other sciences 

 are bequeathed to the parish library of Alford for the use of the 

 district ; and all remaining funds are to be safely invested and the 

 interest to be devoted for all time to the foundation of certain 

 prizes, to be called by his name, for the promotion of the study 

 of natm-al science, especially botany, amongst the children in 

 certain parishes in and round the Vale of Alford. A memoir 

 of the old man is now being written by Mr. Jolly, aud will be 

 anticipated with interest. 



