414 



Dr. 



Oliver Lodge on 



Opacity. 



" Therefore 50 metres is the distance in which the attenuation 

 due to conductivity is in the ratio 2*718 to 1, and there is no reason 

 why the conductivity of sea-water should interfere, if the vahie is 

 like that assumed above. 



"These formulae and results were communicated by me to 

 Prof. Ayrton at the beginning of last year, he having enquired 

 regarding the matter, on behalf of Mr. Evershed I believe. 



" The doubtful point was the conductivity. I had no data, but 

 took the above I' from a paper which had just reached me from 

 3Ir. Zeeman. Xow Mr. "Whitehead uses fr- 1 = 20 10 , which is no 

 less than 15 times as great. I presume there is good authority for 

 this datum *. Xone is given. Using it we obtain » 1 = 13 1 16 . 



" Thus 50 metres is reduced to 13-16 metres. But a considerably 

 greater conductivity is required before it can be accepted that the 

 statements which have appeared in the press, that the failure of 

 the experiments endeavouring to establish telegraphic communica- 

 tion with a light-ship from the sea-bottom was due to the con- 

 ductance of the sea, are correct. It seems unlikely theoretically. 

 and Mr. Stevenson has contradicted it (in 'Nature') from the 

 practical point of view. So far as I know, no account has been. 

 published of these experiments, therefore there is no means ol 

 finding the cause of the failure." 



Appendix II. 

 The experiments of W. Wien on the transparency of metals, 

 bv means of a bolometer arranged to receive the radiation from a 

 bunsen burner transmitted through different films, resulted in the 

 following numbers for the proportion of radiation transmitted. 







Proportion transmitted. 





Metal. 



Thickness in 

 10~ : centim. 



Bunsen burner 



Bunsen burner 



Proportion 

 reflected. 







luminous. 



non-luminous. 



•13 



Platinum 



20 



•32 



•37 



Iron & Platinum 



404-20 



•10 



■14 



•45 



Gold 1 



56 



•040 



•041 



•63 



Gold2 



100 

 24 

 35 

 36 



•0035 

 •41 

 •20 

 •058 



•0036 



•41 

 •20 

 •046 



•80 

 •05 

 ■19 

 •78 



Gold 3 



Gold 4 



Silver 1 (blue) ... 



Silver 2 (grey) . . . 



39-5 



•058 



•055 



•60 



Silver 3 (grey) . . . 



29 



•25 



•42 



•40 



Silver 4 (blue) ... 



59-7 



•0022 



•0019 



•95 



Silver 5 (grey) ... 



27-3 



•31 



•43 



•24 



* Dr. J. L. Howard has recently set a student to determine the resistivity 

 of the sea-water used by Professor Herdman, density 1-019 gr. per c.c, 

 and he finds it to be 3x 10 10 c.g.s. at 15° C— O. J. L*, March 1899. 



