NATURAL PHILOSOPHY. 105 



statical values of all these varieties were tested by a separate appa- 

 ratus, called the axial galvanometer. Twelve varieties in all were so 

 tested, in bars of uniform size, one foot in length, and one inch in 

 diameter, and it was found that the statical and dynamic properties 

 corresponded.) 4. The proportions of the helices, approximately, 

 though much remains unsettled upon this important point. 5. The 

 advantages of keeping up the magnetism in the axial bar. 6. Vari- 

 ous modes of reversing the motion of the engine, and with success. 

 7. Various kinds of cut-off (which is the most critical and important 

 point in the construction of the engine). 8. The operation of closed 

 circuits and secondary currents was tested with great care and accu- 

 racy. 9. The best working velocity of this engine, and its absolute 

 power with a given battery. 10. The ratio of increase of power, 

 with an increase in the quantity of the current. 11. The values of 

 different kinds of metal in forming the cut-off. Various other minor 

 points were also the subject of experiment, after which experiments 

 were commenced upon a larger scale, with a view to determine 

 whether the same proportion of pow r er could be obtained from large as 

 from small engines, this being the principal question in view at the 

 time of the appropriation. A large number of helices were construct- 

 ed, of various sizes, and suitable bars of soft iron, corresponding to 

 the helices, both hollow and solid, from two inches to eight inches in 

 diameter, and generally three feet in length, were prepared. There 

 were also some bars of four and five feet in length. With these bars 

 and helices a multitude of experiments were performed and recorded 

 daily for about two months. They were not such as could be per- 

 formed upon the laboratory table ; but were made with masses of iron, 

 weighing in some cases three hundred pounds, and helices sometimes 

 twice that weight. 



" Adhering to the same size of battery through a long course of 

 experiments, and varying the coils and bars, I found, to my great 

 gratification, that, as I increased the dimensions of each, a correspond- 

 ing increase of power was exhibited, and the consumption of material, 

 or the cost of the power, in some proportion diminished. These re- 

 sults fully justified the undertaking at once of an engine upon a much 

 larger scale than any hitherto tried. This engine was an upright en- 

 gine of two feet stroke ; and in order to have facilities for comparative 

 trials and experiments, it w T as necessary that a double engine should 

 be made, the two parts exactly corresponding. Two bars of soft iron, 

 six inches in diameter and three feet in length, were the prime mov- 

 ers, and these were balanced by means of connecting rods and cranks 

 upon a fly-wheel shaft. The balance-wheel and shaft together weighed 

 six hundred pounds. When this engine was first tried, with the same 

 battery which had before given me one fifth of a horse-power with a 

 smaller engine, it produced only one third of a horse-power. By care- 

 ful attention to the adjustments, and particularly to the cut-off, which 

 was a very different thing now from what it had been in smaller en- 

 gines, the engine soon yielded one horse-power. Here was a gain of 

 eighty per cent., as measured merely by the size of the battery. But 

 it was much more ; for the cost was found to be less for one horse- 



