Double Avial Reciprocating Engine. 139 
of the applications of galvanism’for the development of magnet- 
ism. ‘The proportions of battery, and length and size of wire, 
and relations of length to diameter of the helices used in the in- 
strument just described seem to be very near correct, and Iam 
indebted for them to Mr. Vail, Prof. Morse’s assistant. I had 
never seen so great a weight sustained within the helix as in one 
of about the size used above, and first kindly shown and loaned 
to me by Mr. Vail. The bar he sustained within a single helix 
by means of 10 pairs Grove’s battery, weighed over half a pound. 
By modifying the proportions, I have succeeded in sustaining 
over three pounds, and believe that even ten times that amount 
may be sustained free of visible support, by proper attention to 
the several ratios required. 
Double Axial Reciprocating Engine. 
Before entering upon the description of this improvement, I 
may be allowed a few remarks as to the nature and design of 
these publications. Conceiving that this, and the first machine 
described, and also the several instruments which I have designed 
upon the same principle of action, form an entirely new era in 
the science of electromotion, (if we except the delicate experi- 
ment of Dela Rive’s ring, and others of the class of electro- 
dynamies,) I have thought that the invention would ultimately, 
and perchance very soon, become one of ‘practical value, and am 
therefore desirous of securing by patent the right to the following 
modifications, viz. the single axial engine, the double axial en- 
gine, and the rotary form of engine, dependent upon the same 
species of action; which last will be hereafter described. The 
galvanometer, being an instrument calculated to be productive of 
great good to science, without any further modification, the gal- 
vanic or magnetic gun, the watchman in his tower, and some 
other interesting contributions to the physique amusante hereafter 
to be mentioned, I give to the public as instruments of philosoph- 
ical research and amusement. Situated as I am, being one of 
the examiners in the Patent Office, it becomes necessary for me 
to take an unusual step, to secure my title to this novel invention. 
By the statute law, no officer in the Patent Office can take out a 
patent for any invention, nor acquire any interest in a patent after 
his appointment to office. Consequently, if one so situated should 
make an important invention, he can have no security as long as 
his invention is known toany second person. As publicity with- 
