488 



Mr. S. Bidwell. On the Lifting Power of [June 10, 



being approached. But it was of greater interest to study the effects 

 produced when both portions of the ring or of the rod were under the 

 direct influence of the magnetising coil. 



The first experiment was made with the divided rod. One portion 

 was supported by means of its hook in a vertical position ; a scale-pan 

 was attached to the hooked end of the other portion, and the flat ends 

 of the two were brought into contact and surrounded by the solenoid. 

 Currents of gradually increasing strength were then caused to pass 

 through the solenoid, and note was taken of the greatest weight 

 which could in each case be placed in the scale-pan without tearing 

 asunder the ends of the two rods. The general results are briefly as 

 follow: — When the intensity of the field at the junction had reached 

 about 50 C.G-.S units, the weight supported was nearly 7000 grams 

 per square centimetre of the section of the rod. After this value was 

 exceeded it became quite evident that the weight which could be 

 sustained was increasing more slowly than the magnetising current, 

 and the proportionate increase became rapidly smaller as the current 

 was made stronger. This state of things continued until the intensity 

 of the field was about 270 units, when the weight supported amounted 

 to 10,800 grams per square centimetre of section. But from this point 

 onwards the magnetising current and the weight that could be carried 

 increased in exactly the same proportion. The rate of increase of the 

 load was, indeed, comparatively small, but it was perfectly constant, 

 and continued so until the field had attained the high intensity of 

 1074 C.G.S. units. Here the experiment was stopped, the greatest 

 weight supported having been 15,100 grams per square centimetre. 



On account of some uncertainty as to the possible influence of the 

 external ends of the divided rod, it was thought desirable to make the 

 experiment with the divided ring, the current being caused to pass in 

 the same direction through the coils surrounding both portions. The 

 general character of the results was the same as before, but the 

 weight supported per unit of area was from first to last somewhat 

 greater. The falling off in the rate of increase of the lifting power 

 was well marked when the intensity of the magnetic force had 

 reached 50 C.Gr.S. units, at which point the weight sustained was about 

 10,000 grams per square centimetre. And it continued to diminish 

 until the magnetic force was 250 units and the weight supported 

 14,000 grams. From this point the increments of lifting power and 

 of magnetic force appeared to be exactly proportional, and continued 

 to be so until the magnetic force had been carried up to 585 units, 

 when the limit of the battery power was reached and the experiment 

 stopped, the maximum weight supported having been 15,905 grams 

 per square centimetre or 226' 3 lbs. per square inch.* 



* As mentioned below, a part of the effect is to be attributed to the action 

 between the coil and the iron. If in respect of this we deduct ^1/^ = 912 grams 



