66 ANNUAL OF SCIENTIFIC DISCOVERY. 



small hammer is attached. This spring 1 , being placed in the teeth of 

 the serrated bar, is relieved by the handle being touched by the fin- 

 ger, which regulates the extent of the sound from the ticking of a 

 watch to the sharp, loud tone of a bell. This instrument tests with 

 great accuracy the amount of hearing actually possessed by a person 

 in every stage of deafness, so that its advantages must be evident to 

 every one. 



*r 



UNIVERSAL SUN-DIAL. 



AT the last meeting of the British Association, the President ex- 

 hibited a universal sun-dial, constructed by a gentleman in Dublin. 

 It consists of a cylinder, set to the day of the month, and then elevat- 

 ed to the latitude. A thin plate of metal in the direction of its axis is 

 then turned by a milled head below it, till the shadow is a minimum, 

 when a dial in the top shows the hours by one hand and the minutes 

 by another. It appears by this that the time can be obtained to the 

 precision of about three seconds. 



MECHANICAL LEECH. 



THIS apparatus, the invention of a Frenchman, consists essentially 

 of two parts, an instrument for puncturing the skin, and another for 

 promoting the flow of the blood by removing atmospheric pressure 

 from the punctured part. The puncture is effected by a lancet, whose 

 blade has the form of the cutting apparatus of the leech. This lancet 

 is fixed in the mouth of a tube, and projects about the eighth of an 

 inch beyond the edge ; it may be elevated by a small lever, so that its 

 point shall be within the tube. Attached to the opposite end of the 

 tube by a piece of vulcanized India-rubber, which acts as a spring, is 

 a piston, which is pressed down by a rod, and on removing the pres- 

 sure is drawn back by the spring. The piston being pressed down, 

 the open end of the tube, in which is the lancet, is placed over the part 

 to be punctured ; the pressure is now removed, when the piston is 

 drawn back by the spring, and, exhausting the air within the tube, the 

 skin is forced up into its mouth. On loosening the lever, the lancet is 

 drawn down by another spring, so as to effect the puncture. The 

 cutting instrument is then removed, and a glass tube with a piston is 

 placed over the puncture, the air within being exhausted so that the 

 tube adheres to the part, and the blood flows freely. A dozen of 

 these tubes, each of which draws as much as a large leech, may be 

 thus attached in two or three minutes. The idea of a mechanical 

 leech is not new, but the use of the India-rubber springs forms the 

 important feature of this new apparatus. London Medical Journal. 



PREVENTION OF MINE ACCIDENTS. 



AT the meeting of the British Association, recently held in Bir- 

 mingham, the attention of the members was invited to a patent ap- 

 paratus, invented by Mr. Foudrinier, for obviating the risks which 

 attend the breaking of the ropes or chains attached to the corves or 



