136 Azvial Galvanometer. 
Art. XV.—Azial Galvanometer, and Double Axial Reciproca- 
ting Engine; by Cuartes G. Pace, Prof. Chem, and iano 
Columbian College, Washington, D. C. ‘ 
The Avial Galvanometer.—As this instrument possesses char- 
acteristics distinguishing it from all others, I have selected for it 
the term azial, as appropriate and in some measure descriptive of 
its character. In all the known forms of galvanometer, the mag- 
netic needle or a bar of magnetized steel is used, to indicate the 
action of the galvanic current, or else the coil of wire itself is 
free to move, while the needle or bar is stationary. In all such 
instruments there is one liability to error from a source not 
sufficiently regarded, viz. the frequent disturbance of the power 
of the needle by the magnetizing power of the current in the 
coil, which, if the needle is in such position as would naturally 
result from the action of the coil, will slowly increase its mag- 
netic power, and if forced by accident or otherwise into a reverse 
position, will diminish its power, and ultimately reverse its po- 
larity, provided the current be powerful and the action continued 
for any length of time. In the new instrument, no permanent 
magnet is used, the motion necessary for purposes of indication 
being made by the action of the coils upon a bar of soft iron. 
Every bar of soft iron retains, after being powerfully magnetized, 
a certain amount of magnetic power; but this, if the bar is not 
very large and hard, is very small, and may be considered as 
nearly a constant quantity. I have sometimes thought that the 
term absolute galvanometer might well be applied to this instru- 
ment, as it immediately indicates by weight the absolute force 
exerted upon the iron bar. JI would not recommend the mount- 
ing of the instrument in the style exhibited in the figure, as the 
sketch is taken from the instrument in its primitive form. Many 
modifications will suggest themselves of modes of constructing 
the instrument, as well as the means of indicating the forces. 
The U form bar 2, 2, Fig. 1, is of soft iron carefully annealed, 
well polished, and graduated to spaces of one sixth of an inch 
upon one of its legs; the diameter of the iron is about one eighth 
of an inch less than the opening in the centre of the helix, to 
allow free play as the helices are raised and lowered, or the mag- 
nets drawn down within them. ‘The bar is suspended by a 
