1895.] 



on the Effects of Electric Currents in Iron, dc. 



549 



Kelvin's syphon recorders, made by Messrs. Muirhead & Co., which 

 will be at work after the lecture, and also an artificial cable, which 

 has also been made by Messrs. Muirhead & Co. Curves can be 

 obtained from the end and middle of the cable. 



Magnetic experiments such as these have really a wide appli- 

 cation. They are not restricted to the particular size of the cylinder 

 upon which the experiment is made. If the cylinder is larger or 

 smaller similar magnetic events will happen, but they will happen 

 at times shorter or longer in direct proportion to the square of the 

 linear dimensions of the cylinders — that is, to the areas of the 

 cylinders. Hence we may boldly infer what will happen in magnet 

 cores of dimensions too small to experiment upon or so large that 

 they would be very costly to make. For example, suppose a core is 



Fig. 12. 



made up of wires x J ¥ of an inch in diameter, we may expect that 

 everything will go on with the same currents around the core but 

 1,440,000 times as fast ; with a force of 24, everything will be over 

 at the centre of the core if the current is instantaneously reversed in 



4 (rtiw of a second. 



One very practical application of these results is to the cores of 

 transformers, but in this case we have not the sudden reversal of the 

 magnetising current, but the current continuously varies from positive 

 to negative and from negative to positive. It is not difficult to 

 imitate these conditions on the slow scale which is suitable for our 

 large magnet, but if I were to show you an experiment at an 

 appropriate rate on the magnet which we used for reversals, I fear 

 you would find the results intolerably tedious. It would take some 

 minutes to get through a single reversal. I will, therefore, use 



Vol. XIV. (No. 89.) <2 p 



