April 1 8, 1878] 



NATURE 



487 



111 the surrounding district, where larks are equally numerous, 

 I have never detected the peoiliar note. 



This power of imitating the songs of birds is well known to 

 bird-fanciers and dealers ; hence birds taken from the nest are 

 considered worthless by those who admire the natural song. I 

 myself had a Siskin that sang the goldfinch's song, and a nuthatch 

 that I sent to a bird show came back with a wonderful medley 

 of notes, of which he seemed extremely proud, the call-note 

 of the canary and several notes of the blackbird being amongst 

 those I could clearly recognise. J. Young 



Notting Hill 



Harrow School Bathing-Place 



Will you kindly allow me to appeal through your columns 

 for suggestions how to cure a nuisance which we suffer from 

 year after year in our bathing-place here, and for which we have 

 as yet found no remedy ? 



'fhe water which is pumped into the bath from a considerable 

 dei>th is beautifully clear at the beginning of the season, but as 

 soon as the weather becomes hot and the rays of the sun attain 

 power, countless filaments, consisting of confervse, &c., spring 

 up from the brick floor of the bath, and push their way rapidly 

 to the surface, the depth of the water varying from about four 

 feet to six feet. As the boys plunge from the side into the water 

 and swim about the bath these long wavy stems are shivered into 

 myriads of fragments, which collect on the surface of the water 

 and form there a disagreeable and ugly scu'v>, which de- 

 tracts not a little from the pleasure of bathing during a great 

 part of the summer term. We have taken some pains to dis- 

 co\er a remedy for this, whether by chemical or other means, but 

 as yet have been quite unsuccessful. The weed reappears in ecpial 

 exuberance year after year and we are helpless. If any of your 

 readers can contribute to the removal of this annual plag\ie, he 

 would confer a great benefit on the school, and any practical 

 suggestions would be gratefully received either by G. Griffith, 

 Esq., Harrow, or by ARTHUR G. Watson 



Harrow, April 8 



London Clay Fossils 



I SHOULD be glad if any of the contributors to Nature 

 would kindly inform me of any fossiliferous sections of the 

 London clay at present open in the immediate neighbourhood 

 of London. Many of those named in Whitaker's " Geology of 

 Londor," such as Ilighgate, Ilampstead Heath, &c., are closed, 

 while others at Lewisham, &c., yield no fossils except a few 

 fragments of wood. Hermann II. Hoffert 



South Kensington Science Schools, April 15 



Meteor 



As the meteor of April 2 was seen at Ashwell, Herts, and 

 with much the same course and splendour .t.s observed at 

 Leicester (but without any accompanying sound), it must have 

 been very much further off than your Leicester correspondent 

 imagines. 



So bright a meteor, falling so early in the evening, cannot 

 fail to have been much observed. H. George Fordham 



Odscy Grange, Royston, Herts 



The Nightingale 



In care you have received no earlier communication to a 

 similar effect, you may possibly think it worth while to record 

 that I heard a nightingale twice on the 14th instant, in a planta- 

 tion by the side of Hanger Lane, in Ealing. It was but an 

 abortive song, such as the first of the season is very apt to be, as 

 if he were rather shy of the sound of. his own voice. But there 

 was enough of it to leave no iwssible doubt as to the identity of 

 the performer. I may add that I have in previous years heard 

 him in tlie same spot two or three days earlier than elsewhere 

 in this neighbourhood. 



I heard the wryneck ("cuckoo's mate") also several times on 

 the same day in Gunnersbury and Hanger Lanes, having heard 

 him once the previous afternoon (13th) in Kew Gardens. 



Gunnersbury, April 16 G, J. Pearse 



FLOATING MAGNETS^ 



"POR one of my little books of the Experimental 

 -*- Science Series I have devised a system of expe- 

 riments which illustrate the action of atomic forces, and 

 the atomic arrangement in molecules, in so pleasing a 

 manner that I think these experiments should be known 

 to those interested in the study and teaching of physics. 



A dozen or more of No. 5 or 6 sewing needles are 

 magnetised with their points of the same polarity, say 

 north. Each needle is run into a small cork, \ in. long 

 and /V ^"' i" diameter, which is of such size that it just 

 floats the needle in an upright position. The eye end of 

 the needle just comes through the top of the cork. 



Float three of these vertical magnetic needles in a bowl 

 of water, and then slowly bring down over them the N. 

 pole of a rather large cylindrical magnet. The mutually 

 repellent needles at once approach each other and finally 

 arrange themselves at the vertices of an equilateral 

 triangle, thus .'. . The needles come nearer together 

 or go further away as the magnet above them approaches 

 them or is removed from them. Vibrations of the magnet 

 up and down cause the needles to vibrate, the triangle 

 formed by them alternately increasing and diminishing 

 in size. 



On lifting the magnet vertically to a distance, the 

 needles mutually repel and end by taking up positions at 

 the vertices of a triangle inscribed to the bowl. 



Four floating needles take these two f jr.ns 



Five 



Six 



Seven ,, ,, „ ... 



I have obtained the figures up to the combination of 

 twenty floating needles. Some of these forms are stable; 

 others are unstable, and are sent into the stable forms by 

 vibration. 



These experiments can be varied without end. It is 

 certainly interesting to see the mutual efifect of two or 

 more vibrating systems, each ruled more or less by the 

 motions of its own superposed magnet ; to witness the 

 deformations and decompositions of one molecular ar- 

 rangement by the vibrations of a neighbouring group, to 

 note the changes in form w-hich take place when a larger 

 magnet enters the combination, and to see the deforma- 

 tion of groups produced by the side action of a magnet 

 placed near the bowl. 



In the vertical lantern these exhibitions are suggestive 

 of much thought to the student. Of course they are 

 merely suggestions and illustrations of molecular actions 

 and forms, for they exhibit only the results of actions in 

 a plane ; so the student should be careful how he draws 

 conclusions from them as to the grouping and mutual 

 actions of molecules in space. 



I will here add that I use needles floating vertically and 

 horizontally in water as delicate and mobile indicators of 

 magnetic actions, such as the determination of the posi- 

 tion of the poles in magnets, and the displacement of the 

 lines of magnetic force during inductive action on plates 

 of metal, at rest and in motion. 



The vibratory motions in the lines of force in the Bell 

 telephone have been studied from the motions of a needle 

 (floating vertically under the pole of the magnet), caused 

 by moving to and fro through determined distances, the 



' A note on Experiments with Floating Magnets, by Alfred M. Mayer. 

 Reprinted from the Ameri«t>i Journal 0/ Science. 



