G. F. Barker—New Vertical-lantern Galvanometer. 209 
essentially the same in principle as the mirror-galvanometer ; 
t it cannot be as sensitive as the latter, while it is open to 
the same objection which we have brought against this—the 
objection of unintelligibility. In the hands of so skillful an 
experimenter as Mayer, it seems, however, to have worked 
admirably. a 
It was a tacit conviction, that none of the forms of apparatus 
now described would satisfactorily answer all the requirements 
of the lecture above referred to, that led to the devising of the 
galvanometer now to be described, which was constructed in 
an attachment to the ordinary lantern, is shown in the annexed 
cut, fig. 1. Parallel rays of light, from the 
lantern in front of which it is placed, are 
received upon the mirror, which is inclined 
45° to the horizon, and are thrown directly 
) 
water-tanks, ete., may be placed and many 
beautiful experiments shown. To adapt this 
vertical lantern to the purposes of a galvan- 
ometer, a graduated circle, photographed on 
glass, is placed upon the horizontal con- 
densing lens. Above this, a magnetic needle, 
of the shape of a very acute rhomb, is sus- 
Inclined mirror, and which carries a second needle near 
* This Journal, IU, ii, 71, 153, July, Aug. 1871; Jour. Frank. Inst., IIT, lxi, 300, 
May, 1871; Quar. J’ Sci.,’Oct. 1871. In Duboseq’s vertical attachment, which 
the bacttised in his catalogue in 1870, the arrangement is similar, except that 
placed above the object 
i ly illumi- 
nated but not very bright field. 
Am. Jour. Sct.—Turrp Serres, Vor. X, No. 57.—SEPt., 1875. 
4; 
