396 Scientific Intelligence. 
center, depends on the different distances of two equal and 
opposite currents. It is evident also that the instrument may 
be used as a simple tangent galvanometer. 
Thus if we call the free ends of the hoops A and B respec- 
tively, and the point of juncture C, by joining up a circuit 
through A and B we get the differential action; but by joining 
up through C and A or B, the action is that of a simple tangent 
galvanometer. If v7 and r’ represent the radii of the outer and 
inner hoops respectively, the ordinary formula becomes 
bre 
2a(r—r’) 
when the instrument is used differentially. 
An instrument has been constructed at the J. C. Green 
School of Science for its Physical Laboratory of dimensions as 
follows: 
x Htand 
Diameter of outer hoop..............- UN Blog 
Siameter Of inher Hoop sn. 6. sie sree o> 9-96 
MVM OF CRO NOOD. tou. oe 8 
Thickness of each hoop... ........... 0-35™ 
The theoretical constant of this instrament agrees very closely 
with that ascertained experimentally by means of the volta- 
meter. The needle which is usually suspended in the center of 
the hoops, may, if desired, in order to measure aang! 
Princeton, March 10, 1881. 
SCIENTIFIC INTELLIGENCE. 
I. CHEMISTRY AND PHySICcs. 
1. On the Chlorhydrates of Metallic Chlorides, —Compounds 
formed by the union of hydrochloric acid with metallic chlorides 
have been described, but they have been very imperfectly studied. — 
Since these bodies appear to perform an important part In certain 
reactions, Berrur.or has investigated them, both chemically and 
thermally. By the prolonged action of hydrochloric acid gas 
upon a solution of cadmium chloride saturated in the cold, a well 
defined and crystallized body CdCl,(HCl),(H,O), is obtained, 
which fumes in the air and loses hydrochloric acid; but since 
cadmium chloride absorbs this gas even when fused the dissocia- 
tion is not complete at a red heat. Thermally CdCl,+(HCl), 
gas +(H,O), liquid, evolves +-40-2 calories; with solid water, 
+30 calories. Bromhydrate of bromide of cadmium and the 
iodhydrate of iodide ot cadmium were also obtained in beautiful 
