148 SCIENTIFIC NOTES. 



Passing from light to electricity, I must confine what I have 

 to say in as small compass as possible, for I have already much 

 exceeded the limits which should have confined my remarks. Sir 

 William Thompson, of Glasgow, has made a remarkable discovery 

 with regard to the working of electric cables, viz., that by 

 properly proportioning the strength of the current, signals may bo 

 got through very much faster than has been supposed to be 

 possible. The maximum rate which ho has obtained in as experi- 

 mental cable of 2,000 miles is 45 words per minute. These are, 

 of course, sent by the automatic sender, and received on a most 

 delicate machine he has contrived, which is capable of writing 

 with excessively weak currents. Some idea of the delicacy of this 

 instrument may be gained from the fact that the pen is a very fine 

 thread of glass, with a capillary tube in it for the ink. This pen 

 is suspended so that the point of it is near but not touching the 

 paper — near enough, however, for capillary attraction to draw the 

 ink on to the paper as the pen moves. To the pen thus hanging 

 freely over the paper a thread is attached, and carried to the light 

 armature that vibrates with the current, and communicates each 

 motion to the pen. The mechanical arrangements were not com- 

 plete when I saw it ; but probably before the end of the year it 

 will be at work, and effect an enormous saving in the expense and 

 trouble of working cables. 



I had the pleasure of seeing his beautiful quadrant electro- 

 meter, and of securing one for use in Sydney. So perfect is the 

 insulation and arrangement of this instrument now, that once 

 charged it may be kept in an ordinary room, and made to keep up 

 its own charge almost indefinitely. In the application of elec- 

 tricity to lightning and electroplating purposes, perfectly marvel- 

 lous results are now obtained by Wilde's, and also by Gramme's 

 machines. Wilde's is, I think, much the more powerful of the 

 two, and is preferred by Elkington for depositing metals, because 

 it deposits faster. With one of Wilde's hand machines I melted 

 five inches of No. 1 9 iron wire with ease ; and in his large machine, 

 which he has recently altered, so that the electricity is produced 

 with a much slower rotation of the armature than that required in 

 his earlier machines, I saw five feet of No. 1 6 iron wire melt away 

 and run like drops of water; and the light yielded by half-inch 

 carbons and 4-horse power engines was magnificent, both in 

 brilliance and steadiness. Gramme's machine also yields a very 

 fine and steady light ; but I believe Wilde's will be selected by 

 the Admiralty, for in some recent experiments made for the pur- 

 pose of testing it at Spithead, it was considered by the officers 

 present impossible for any vessel to come within three miles of a 

 fort armed with one of these lights without being seen, so that she 

 could be fired upon even in the darkest night, rain and fog excepted. 



