330 Gahano-Mugnttic Apparatus of Prof. Dana. 



I visited him soon after the shock, and witnessed the de- 

 moHshing effects of the lightning. The place where it 

 struck is a projection of one story, at right-angles with the 

 house, which is two stories high, and within a few feet of 

 their junction. Mr. R, was in the house at the tinne. It 

 was rather difficult to decide whether the lightning ascend- 

 ed or descended — the appearances rather indicated the lat- 

 ter. The side of the building was laid nearly bare of its 

 covering, from the eaves to the ground; and most of the 

 nails in a contiguous door were started, and one window 

 near the angle with the house was completely shivered, and 

 the glass thrown outward^ I suppose by the concussion, and 

 the pressure of the air or fluid with which the apartment 

 was filled. Much smoke and sulphureous smell were ob- 

 served on entering this apartment. The point at the eaves 

 where the first vestiges of the lightning were perceivable, 

 was directly under the branches, and but three feet from 

 the trunk of a lofty poplar, which remained unhurt — thus 

 affording an additional proof to what is stated in your No. 

 for June last, that this tree is a poor conductor and no 

 safe-guard against lightning. I would remark also, that 

 there was a good rod to the house, sixty-three feet distant 

 from the smitten spot. 



Art. XV. — Galvano-Magnetic Apparatus of Prof. Dana. 



(See Figure 6 in Plate 12 at the end.) 



A, is a cork through which passes a strip of sheet copper 

 C, about one quarter of an inch wide and eight inches long, 

 bent at the bottom like the letter U, so as partly to inclose 

 the strip of sheet zinc Z, of the same width as the copper; 

 NS is a steel wire five inches long, around which passes 

 about seventy-five turns of brass wire. One end of this 

 passes through a perforation in the upper part of the cop- 

 per, and the other through a similar perforation in the 

 zinc. The brass wire is covered with sewing silk; when 

 his little apparatus is placed in a tall glass jar containing 

 water, acidulated with sulphuric or nitric acid, the wire 

 NS soon arranges itself in the plane of the magnetic meri- 

 dian ; the steel wire becomes a temporary magnet, and will 



