36 ANNUAL OF SCIENTIFIC DISCOVERY. 



the top, by a screw joint, and again on the top of the glass tube is fitted a 

 strong hollow copper ball by a similar screw joint. The lower tube, 

 which we will call a, has a well-turned piston fitted to it, from which runs 

 a rod which is only a trifle longer than the tube, a, and just enters the 

 tube, b, when the piston is at its lowest point. A well-made spring is 

 placed in the tube, a, above the piston, and the tube, a, being narrowed at 

 the top so as just to admit the free passage of the rod, and the rod having 

 a little button at its top the piston is kept at its lowest point by the spring, 

 except when sufficient pressure is applied from below to compress the 

 spring. The glass tube has a small ring fixed in it, just so as to stick at 

 any point to which it is pushed, and the button at the top of the rod 

 serves to push the ring straight, and the ring thus forms an index of the 

 degree to which the spring has been compressed. The ball on the top 

 serves as a mere reservoir of air to equalize the action of the apparatus as 

 much as possible. The whole of this apparatus is enclosed in a wire cage, 

 for the sake of protection from blows. To graduate this apparatus, I let 

 it down in a known depth of water, say ten fathoms, and having observed 

 the point to which the ring in the glass tube is pushed, and having marked 

 this point off, the ball is to be unscrewed, and with a small ramrod the 

 ring is to be pushed down till it rests on the top of the piston rod. The 

 ball being replaced, the apparatus is sunk in twenty fathoms ; after a sim- 

 ilar manner it is sunk in thirty, and next in forty fathoms. This will test 

 the accuracy of the apparatus ; and the marks made on the glass tube, b, 

 after each trial, will give a scale from which the whole tube may be grad- 

 uated, even to thousands of fathoms, if the tube be long enough or the 

 spring strong enough. I have been induced to make this communication 

 011 account of the great use which may be made of such an apparatus. 



SHOAL WATER INDICATOR. 



Mr. Edwards, of her Majesty's dock-yard, Pembroke, has recently pat- 

 ented an invention which is to indicate when a vessel, under steam or can- 

 vas, comes into water at any given depth. The apparatus is to be employed 

 chiefly in fogs and at night time, and is intended to afford a more certain 

 means of ascertaining when the vessel employing it is nearing a coast or 

 shoal, than is provided by the ordinary soundings. This invention con- 

 sists of a copper or iron rod, about three-fourths of an inch in diameter, 

 and of any desirable length say three fathoms. This rod is attached by 

 an eye or other contrivance to the under side of the keel, and is kept in a 

 vertical position by the stays, to which a grapnel and weight are attached, 

 by a line, and which is secured on board the vessel to a lever that has 

 connected to it a weight sufficiently large to counteract the tension pro- 

 duced upon the line by the resistance of the water against it. By means 

 of this, line soundings may, if deemed necessary, be taken, the ordinary 

 lead line being dispensed with. When the rod or grapnel takes the 

 ground, the line slipping from the lever will cause the reel to revolve, 



