1903.] 



Some Experiments in Magnetism* 



5 



much of the internal organisation of Ferns, which were reproduced by 

 means of seeds. At present, the families Lyginodendrese and 

 Medullosese may be placed, with little risk of error, in the new class, 

 Pteridospermaa. 



" Some Experiments in Magnetism." By T. C. Porter. Com- 

 municated by Lord Kayleigh, O.M., F.B.S. Eeceived 

 November 9,— Read November 26, 1903. 



[Plate 1.] 



For many years the writer has, from time to time, been engaged in 

 studying the effect of a powerful magnetic field upon crystals in the 

 act of their formation and growth. It seemed to him probable that if 

 the molecules of substances have magnetic poles, they might group 

 themselves differently when under the influence of a powerful magnetic 

 field, thus producing an orientation of the crystals, or even an altera- 

 tion in the form or optical characteristics of the crystals themselves. 

 It seemed also possible that if the supposed polar properties of the 

 molecules were the result of atomic polarity, a powerful external magnet 

 might produce some appreciable effect in the chemical combination of 

 the atoms, changing the rate of chemical reaction, if it did not change 

 Ihe character of the compounds formed. Many effects were observed, 

 and were at first erroneously attributed to the influence of magnetism ; 

 later, when, by specially contrived apparatus, the influence of variation 

 in temperature, humidity of the air, and above all of the history and 

 character of the surfaces upon which the crystallisation took place, were 

 investigated, these effects were one after another traced to causes other 

 than magnetic, so that the results must, on the whole, be taken as 

 negative. Cases of orientation of crystals growing in the magnetic 

 field and watched under the microscope from their first visibility till 

 they had attained considerable size, such cases of orientation were 

 found in two compounds of iron, but even these orientations were 

 found to depend, at any rate in some cases, upon the direction in 

 which the surface of the glass slide had been rubbed before cleaning 

 for the experiment. The main result of this long, difficult, and 

 expensive research has only been to prove that if there be any such 

 effects as those looked for, they require, to show them indisputably, more 

 powerful fields than those of the very powerful electro-magnets used 

 by the writer. 



A photograph of the orientation of Marignac's basic sulphate of 

 ammonium and iron 3Fe 2 03.5(NH 4 ).20.12S03.18H 2 is given with this 

 paper. 



