160 Scientific Proceedings, Royal Dublin Society. 



A rheotome at tlie home station puts the wire leading to e, e for 

 a moment into circuit with a battery.' If the platinum wire j3 is 

 in its highest position, as it should be, and hence in contact with 

 n, the current will, during the first instant, return bj the wire 

 common to n and to ih.Q thermometer — i.e. by wire No. iii. This 

 fact is known at the home station by the deflection of a galvano- 

 meter in circuit with wire No. iii. The magnet e, e, however, im- 

 mediately attracts up an armature attached, to the arm i. This 

 arm is hinged at one extremity ; at the other it carries a smooth 

 steel pallet, x. The pallet, on moving forward, engages with one 

 of the triangular teeth, turning the wheel through such a distance 

 that a second pallet, g, just gets over another of the teeth, and, on 

 the current being turned off, and the first pallet being restored to 

 its neutral position by the agency of the spring 2, completes the 

 turning of the wheel through one tooth. One make and break, 

 then, of the rheotome serves to turn the wheel and screw by ^oi^x. 

 of a revolution (as there are twenty teeth provided). The screw, 

 however, has a pitch of -yo^^ of an inch ; hence a motion down- 

 wards of "awth of an inch has been imparted to the wire p. The 

 weight P has also been raised through a certain distance. A 

 second make and break of the rheotome urges the wire downwards 

 by another xot^^ of an inch ; and so on. Ultimately, when the 

 wire reaches the mercury in the thermometer, a second deflection 

 of the galvanometer on wire No. iii. in the home station takes place. 

 The number of contacts made is read on the rheotome, and the 

 height of the thermometer deduced. 



Contact is now made for a few seconds between wire No. ii. 

 and the battery. ' The effect on the instrument is, that by the 

 motion of the arm i towards the electro-magnet e', e\ the pallet x, 

 moving backwards, lifts the second pallet, g, out of the wheel, and 

 so liberates the wheel to the action of the weight P. The limb/ 

 and wire p are consequently run up to their highest positions, on 

 attaining which a deflection of the galvanometer once more occurs, 

 and the observer in the home station breaks contact. 



The object of having the wire p hung loosely on the arm /, 

 instead of having it firmly attached to it, is probably apparent. 



' If the instrument be very far removed from the home station, a relay to supply 

 the necessary current to the electro-magnets will be required. 



