234 Gunnery : — ExperimeJits at IVoohvich. 



steeples and lofty edifices, that even myriads of points and pro- 

 minences are not sufficient in all cases to exhaust a thunder 

 cloud of its electricity. Neither are thnnder-stornis ohserved 

 to be unh-equent in situations where the.«e causes are operating, 

 comparatively, to the greatest possible extent. 



Many other objections might be stated: but as the question is 

 proposed merely as a subject tor inquiry, it appears unnecessary 

 to pursue it further. The statement of M. Van Mons appears to 

 advance a circumstance in itsfavour ; but it does not appear to 

 be given as a fact he has observed himself, and is certainly not 

 supported by any correct observations vvhith which I am ac- 

 quainted. 



London, Sept. 14th, 1S15. G. J. Singer. 



P.S. In the last number of this Magazine it is stated, that 

 Professor Dobereiner obtained an amalgam of mercury and hy- 

 drogen, by decomposing water in contact with negative mercury, 

 and that no gaseous hydrogen was liberated. I have made such 

 experiments with every attention I could devise, but have not 

 been able to detect any apparent change in the mercury; and in 

 every case hydrogen has been given off at its points of contact 

 with the water. The experiment is not perhaps accurately 

 described. 



gunnery: EXPKRIMENTS AT WOOLWICH. 



We are glad to learn that experiments on this interesting sub- 

 ject, analogous to those which were conducted some years ago 

 by Dr. Hutton with so much ability and success, are now carry- 

 ing on at V/oolwich — Dr. Gregory of the royal military academy, 

 having been associated with a cojnmittee of general and other 

 officers of artillery, for that purpose. 



In the determination of the initial velocities of projected balls, 

 the ballistic pendtilutn is the instrument which has been hitherto 

 most advantageously employed. Mr. Robins, its original in- 

 ventor, in the experiments described in his Gunnery, made use 

 of a ballistic ])endulum which weighed very little more than half 

 a hundred weight. In the experiments made by Dr. Hutton, the 

 ballistic pendulums were of various sizes and weights, increasing 

 gradually from 560 pounds to 2420 pounds in weight, according 

 to the size of the projected ball, of which the largest was six 

 pounds. The pendulum recently constructed in the royal arsenal 

 at Woolwich considerably exceeds in weight and dimensions the 

 largest that was employed in Dr. Button's experiments. Its 

 weight, at the commencement of the expeiiments, was about 

 7400 pounds, or moie than three tons and a qunrtt-r. The face 

 of the block of timber which forms the core of the pendulum is 

 3 feet broad and 4 feet high, its horizontal length or thickness 



being 



