170 ANNUAL OF SCIENTIFIC DISCOVERY. 



complete circle. The second part consists of a metallic thermom- 

 eter, in which the unequal expansion of two different metals is 

 made to move a lever or pin around a graduated circle which 

 marks the degrees of temperature. .The two parts are in such 

 proximity that the telegraphic lever in passing around the circle 

 must, at some point, come in contact with the pin, which is moved 

 by means of the expanding or contracting metals. This contact 

 breaks one circuit and completes another, and thus transmits to 

 the other extremity of the telegraphic line information of the 

 particular degree of heat at that instant indicated by the ther- 

 mometer. 



A Neutral Magnetic Chamber. Faraday has shown that if a 

 small cubical space be enclosed by arranging square bar magnets, 

 with their like poles in apposition, so as to form a chamber, 

 within that space all local magnetism inferior in power to the 

 magnets employed will be neutralized. The same effect may be 

 obtained with electro-magnets as with permanent magnets, and it 

 is proposed in the "Mechanics' Magazine " thus to enclose the com- 

 pass of an iron ship, as a remedy for the deviation by local attrac- 

 tion. A battery might be constructed to be excited by the sea 

 water flowing through it, requiring no attention as long as the 

 zinc plates lasted. 



A Neiv Bullet Detector. A very ingenious piece of mechanism 

 for the detection and extraction of bullets in wounds has been de- 

 vised by Mr. Sylvan De Wilde. The probe, consisting of two steel 

 wires insulated from each other, is connected with an electric 

 horseshoe magnet and a bell, and when (introduced into the 

 wound) it touches the bullet the circle is completed and the bell 

 rings. The forceps act on the same principle, and are intended 

 first to detect, then to seize, the bullet. They have curved points, 

 and not pallets or spoons. The points of the probes are kept 

 sheathed on introduction to a wound, and not uncovered until the 

 supposed bullet is felt. This is effected by means of a sliding 

 tube. Mr. De Wilde's probe is a sensitive artificial finger, which 

 enters deeply into the tissues, and gives the signal at once when 

 it detects the hidden source of mischief below. London Lancet. 



Magnetism of Gaseous Substances. M. Chautard, professor of 

 natural philosophy at the Faculty of Sciences of Nancy, sent to the 

 Academy of .Sciences a paper on certain experiments of his re-, 

 luting to the magnetism and diamagnetism of gaseous substances. 

 He uses a large Ruhmkorff s electro-magnet, arranged for Fara- 

 day's experiments, and excited by from 25 to 30 Bunsen's ele- 

 ments. Taking Plateau's mixture of soap-suds and glycerine, 

 and blowing it through a pipe so that the bubble formed on one 

 of its extremities may be above the pole of the magnet, :it a dis- 

 tance of from 2 to 3 millimetres, while at the other extremity of 

 the pipe there is a bladder filled with oxygen, from which that 

 gas may be supplied to the bubble, M. Chautard casts a quantity 

 of light from an oxy-hydrogen lamp on the bubble in question, 

 which then moves to and fro like a magnetic pendulum, its oscil- 

 lation having, under these circumstances, been distinctly seen by 

 upwards of oiiO spectators. 



