The Satellites of the Mercury Lines. 443 



It appears to me to be worthy of remark that in no case is 

 the opacity o£ the resonator plate greater for the long waves 

 than for the short, in other words, each sphere is able to stop 

 only that portion of the energy of the wave-front which falls 

 upon it, in other words it does not drain the region sur- 

 rounding it. This rather surprised me, for I had expected to 

 find that with spheres of a certain size we should have 

 moderate transparency for short waves and absolute opacity 

 for the lono; ones. 



I have been unable to find any investigation, either 

 theoretical or experimental, of the action of spherical metal 

 obstacles arranged in close proximity _, upon electromagnetic 

 waves, so that there is nothing with which to compare these 

 results at the present time. 



Investigations have, however, been made with linear rect- 

 angular resonators, and I accordingly commenced experi- 

 menting with these. Silver was deposited on quartz and 

 ruled into small squares with a dividing-engine, but I found 

 that the film was quite as opaque to the 112 /jl waves after the 

 cross ruling, as before, though the size of the squares was less 

 than 1/10 of the wave-length. A photograph of the film 

 with one set of rulings is reproduced on PI. III. fig. 8. 

 This I have alluded to in a previous paper on Electron Atmo- 

 spheres of Metals (Phil. Mag. Aug. 1912). It was found that 

 the ruling had not altered the conductivity of the film, though 

 the microscope indicated that the diamond had cut clear 

 through the silver down to the quartz. If the conductivity 

 is not affected we should not expect the opacity of the films 

 to be decreased. The question as to why the conductivity 

 is not affected was discussed in the previous paper. In order 

 to obtain satisfactory results with resonators prepared in this 

 way, it will be necessary to devise a way of making wider 

 cuts, and leaving less metal between them, and experiments 

 in this direction are now in progress. 



XLVII. The Satellites of the Mercury Lines. By R. AY. Wood, 

 Professor of Experimental Physics, Johns Hopkins University, 

 and Adams Research Fellow of Columbia University *. 



[Plate TV.] 



T INHERE have been many discrepancies among the obser- 



JL vations, made by different observers, of the structure of 



the mercury lines, and even at the present time, with all of 



the work which has been done with echelons and interference 



* Communicated bv the Author. 



