l66 PHILOSOPHICAL TRANSACTIONS. [aNNO I667. 



placed as in the former experiments, and charged with the ordinary charge of 

 powder, or rather with that quantity which by the former experiments shall be 

 found the best ; and being discharged, the fall of the bullet is to be marked, 

 and the distance measured as has been before suggested. 



2. Then try her with less and more powder as before. 



3. Then cut off two inches of the muzzle with a saw, and try as before, do- 

 ing every thing in the same manner : And so cut off still for new trials, till the 

 shot begin to fall shorter than before. 



4. The same may done with guns of different bores. And every experiment 

 to be repeated three or four times, in order always to take a medium among 

 them.* 



Magnetical Experiments. By Mr. Sellers. N" 26, p. 478. 



Mr. Sellers states, that he had often made trial with many needles, touching 

 them on each hemisphere of the stone, in all variety of ways he could imagine, 

 to find if it were possible, by that means, to cause any of these needles to vary 

 in its direction: but that he always found the contrary, all of them conforming 

 to the magnetical meridian, and standing north and south, as other needles that 

 were touched on the very pole of the stone. He adds, ■ that some of these 

 experiments he tried in London, when there was no variation known. 



That on frequent trials of touching needles with different load-stones of seve- 

 ral magnitudes, as also of different virtue; the needles touched gave all of them 

 the same directions. This he thinks is confirmed by all the needles and sea com- 

 passes made in several parts of the world, and consequently touched on several 

 stones of different countries, yet all agreeing in this magnetical harmony, that 

 they all give the same directions. That having sometimes drawn a needle only 

 over the pole of the stone, within the sphere of its virtue, without touching the 

 stone, it has received the same directive quality from the stone as if it had been 

 really touched on the stone itself, though not altogether so strong as if it had 

 touched the stone. Again, that having touched needles on the stone with 

 faint strokes, and other needles with stronger, all these needles received the 

 same effect from the stone, both for strength and direction ; he conceiving that 

 it is not the fainter or stronger touches on the stone, nor the multiplicity of 

 strokes, that varies the needle's strength or direction, but that the nature of 

 the steel whereof the needle is made, and the temper that is given thereunto, 



* A much better way of making all such gunnery experiments, is by means of tlie ballistic pen- 

 dulum, invented by Mr. Robins } of which an account will be given in tlie proper place in lliese 

 Transactions. 



