Si8 Mr. Barlow on the temporary magnetic effect 
Being however thus urged to the inquiry, as well by my 
own speculative views as by your query, and encouraged by 
Mr. Christie’s results, I resolved to put the idea to the test 
of experiment, and to attempt it at once upon a scale that 
should decide the question in the first instance. 
As soon as I had determined upon the experiment, I found 
an excellent opportunity of making the first trial, through 
the kindness of Generals Cuppage and Millar, of the Royal 
Artillery, who gave me permission to have a 13 inch mortar 
shell fixed to the mandrel of one of the pow’erful turning 
lathes worked by the steam engine in the Royal Arsenal. 
This having been done, and the compass properly placed near 
the shell, I turned the shell slowly round, in order to ascertain 
whether in this case, as in Mr. Christie’s, there were any 
effects depending on a change of position ; but if there were 
any, it was so small in the cast iron shell as not to have been 
rendered sensible with the small compass I employed. The 
wheel being now put in geer, the shell commenced its revo- 
lutions at the rate of 640 per minute, and the needle wqs 
deflected out several degrees, at which it remained perfectly 
stationary while the ball was in motion : but it returned imme- 
diately to its original bearing as soon as the motion ceased. 
I now inverted the motion of the shell, and the needle was 
deflected about the same quantity the contrary way, observ- 
ing a similar steady direction as in the former case ; but as 
before, it returned to its original bearing the moment the 
motion was discontinued. 
These experiments were repeated several times before 
some scientific officers of the artillery and engineers, always 
with the same results. 
