452 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



tations have to be made and a table or scale arranored with ffreat 

 labor for each individual galvanometer, in order to make it availa- 

 ble for any valuable purpose. 



The expense and difficulties attending all such methods are such 

 as to render them unavailable for men of ordinary means who 

 cannot afford the requisite time and money. 



To measure the resistance of a magnet or coil by the anthistome- 

 ter, I put it in connection, between the two front screw cups at 

 the left hand end of the rheostat; the galvanometer being con- 

 nected between the screw cup at the right-hand end and one pole 

 of the battery, while the other pole of the battery is connected 

 with the rear cup at the left end. Now, if we turn the left hand 

 switch to the left, the current goes through the thing to be meas- 

 ured, but if we turn it to the right, it goes through the coils of 

 the rheostat. The resistance of these coils are designated by the 

 tigiires over the several switches on the front as the equivalent of 

 miles and fractions of a mile. I now turn the current upon the 

 thino- to be measured and observe to what desree the needle is 

 deflected, and then turn it upon the rheostat and switch in resist- 

 ance until the needle settles at the same degiee. The sum of the 

 numbers at which the switches now stand gives the resistance. 



The switch which turns the current upon the magnet and back 

 on to the rheostat, also the graduated bar and coil which measure 

 hundredths of a mile, are inventions of my own, which give great 

 facility in taking nice and accurate observations. 



I have also discovered a new method of determining the resist- 

 ance of a battery by the antldstometer. To do this I put a cup in 

 connection, as I do a magnet whose resistance I wish to measure. 

 The switches being all at 0, the needle deflects to — say 70 deg. 

 30 min. I now turn the current through the cup, the action of 

 which being added to that of the main battery, the needle deflects 

 to 72 deg. 40 min. I now reverse the current through the cup, 

 so that its action opposes that of the main, and the deflection is 

 65 deg. 55 min. The tangents of the two extreme deflections are 

 3.204 and 2.237, which, being added and their sum divided by 

 two, gives 2.720 for the mean tangent, of which the corresponding 

 degree is 65 deg. 50 min.; by now turning the current through 

 the rheostat and drawing the graduated bar to .20 the needle 

 Gomes to the same degree (69 deg. 50 min.) The resistance of 

 the cup is therefore .2 mile. In comparing two magnets for deter- 

 mining their relative working qualities, I remove the galvanome- 



