498 Sir Oliver Lodge on the 



permeability, and therefore of etherial density, to be expected, 

 was too insignificant to be of appreciable use. Besides, the 



oxidation i)i' the sulphate and the comparative opacity of the 

 perchloride, made these Liquids very difficult. 



21. It is the experiments with air ou which I place most 

 reliance j and of these the best and final determinations were 

 made >i\ months Later, immediately after receiving the following 

 two Letters Erom Dr. Larmor, which 1 am permitted to quote. 

 The first Letter seems to initiate the idea that 1 should try the 

 effect of a longitudinal field on light ; but I had already 

 been trying it within the previous year — as just described — 

 among many other things in the course o£ my " aberration " 

 work. 



Extracts from Letters from Dr. Larmor. 



11 28 Oct., 1893. 



•• four kindness in sending me a copy of your Aberration 

 paper encourages me to ask you a question which now interests 

 me very keenly, namely, whether transmission along lines of 

 magnetic force in air appreciably alters the velocity of light. 

 I cannot discover that anyone has tried, but according to an 

 setherial theory which I have nearly finished writing out, and 

 which covers, I fondly imagine, a very extensive ground, 

 there ought to be such an effect. Perhaps you know, or could 

 easily try with your machinery." 



1 BUppose I replied that Iliad tried, and found nothing, but 

 that I would repeat the trial more carefully if he would be 

 satisfied with an experiment in air; for his next letter says : — 



"1 Nov., 1893. 



" 1 can correlate most things in one scheme if I am allowed 

 that magnetic force is velocity of the aether. . . . A magnetic 

 field should carry the light along with it, — with what kind of 

 velocity 1 have not yet formed an opinion ; but it has nothing 

 to do with rotary effect, and should be of the same order in 

 vacuum a- in a mass." 



11. In the experiment now to be described, as recorded in 

 inv laboratory note-book for November 1893, the light was 

 sent four times round, in opposite directions, through the 

 square of bobbin- above described ; the fact of four times 

 being carefully tested, and sharp broad interference-bands 

 being obtained. A line micrometer cross-wire was seton the 

 middle band, and watched, while 110 volts were applied to 

 each eoil. put on. <>H". reverse, on, off, &c. No shift whatever 

 was seen, either of the middle or any other band — no effect 

 at all. Repeated carefully several times, and watched for so 

 little as the ^th of a band shift, which previous experience 



J 



