534 



Mr, Shelford Bidwell 



[March 11, 



deep, mounted upon a horizontal spindle, upon which is cut a screw 

 having sixty-four threads to the inch. This works in two bearings 

 4 inches apart, one of which has an inside screw corresponding to 

 that upon the spindle. At a point midway between the two ends of 

 the cylinder a pin-hole H is drilled, and behind the hole a selenium 



Fig. 3. 



cell S is fixed. One terminal of the selenium cell is connected 

 (through the spindle and stand of the instrument) with the negative 

 pole of a battery B', the other with the line wire M to the distant 

 station. The receiving instrument X contains a similar brass cylinder, 

 similarly mounted. A platinum point P presses gently upon its sur- 

 face, and is connected both to the line wire and, through a variable 

 resistance E, with the positive pole of a local battery B, the negative 

 pole of which is connected through the galvanometer G with the 

 cylinder. A wire or earth connection N, between the negative pole of 

 the local battery and the positive pole of the other, completes the 

 arrangement. 



To prepare the instruments for work the cylinder of the trans- 

 mitting instrument is brought to its middle position and a picture not 

 more than 2 inches square is focusscd upon its surface by means of 



