440 Mr. W. P. Johnston on a Method of 



diameter, and from 6 inches to a foot long, and having a part 

 of it contracted smoothly and evenly to about a fourth of its 

 diameter, by blowing through it. If the tube be bent upon 

 itself at the point of contraction, the sounds are more readily 

 obtained, though not of greater intensity. 



Apparatus for showing Absorption of Heat on Liquefaction 

 of Solids. 



In a differential air-thermometer, the usual flasks are re- 

 placed by others which have had their bottoms softened, and 

 then introverted to form a cup or basin. In this latter water 

 is placed, and the solid then added. Any change in the liquid's 

 temperature is at once communicated to the air-space round 

 the cup. 



Experiment showing the Expansion of Glass by Heat, and its 

 low Conducting-power. 



A glass tube of -^-inch bore and 18 inches long is bent into the 

 form of a violet-leaf — its free ends forming the apex, and 

 leaving an interval in which a coin may be held by the elasti- 

 city of the glass. When heat is applied to the convex side of 

 the middle bend, the limbs open and the coin falls. 



LYII. On a Simple Method of identifying a submerged Tele- 

 graph- Cable without cutting it. By W. P. Johnston, Offi- 

 ciating Electrician, Indian Government Telegraphs* '. 



CIRCUMSTANCES having arisen which rendered it de- 

 sirable, and at times absolutely necessary, to be in pos- 

 session of a method for identifying a submerged telegraph- 

 cable by applying certain tests to the protecting guards, the 

 following experiments were made for the purpose. 

 The particular case referred to me was this : — 

 " How with two cables (one good and one faulty) across a 

 river, both cables having similar guards, can one be distin- 

 guished from the other without cutting, when either one of 

 them has been raised from the bottom onto the repairing-boat ? 

 The boat being a small one, and the river running rapidly, it 

 becomes difficult and dangerous to cut the cable in the first 

 instance; and to make a joint simply for the purpose of iden- 

 tification is above all things to be avoided." 



My first idea was to attach a very sensitive instrument to 

 the guards where they were raised out of the water, to signal 



* Communicated by Mr. Louis Schwendler. 



