tSEFUL NOTICES. 113 



ill. The mariner who understands well the above principles Practical rt- 

 and theory, will be led to the following steps : guIt> 



1st. To cast overboard such things as will not float, and care- Throw the 

 fully to reserve every thing that will float, for by them tte ship oveJboard^ 8 

 may at last be buoyed up. 



2nd. Empty every cask or thing that can be made water Empty the 

 tight, and put them in the hold, and fasten them down under casks, and 

 water, filling the vacancies between them with billets of wood, U p" gt emw * u 

 even the spars and mast may be cut up for this purpose in des- 

 perate cases, which will fill the hold with air and light matter, 

 and as soon as the water inside is level with that outside, no 

 more will enter : if every hogshead buoy up 875lbs. they will be 

 a great help to sustain the ship, (but care must be taken not to 

 put the empty casks too low, which would overset the ship) 

 and she will float, although half her bottom be torn off. Mari- sj,; ps are sa f er 

 hers for want of this knowledge often" leave their ships too soon, than boats. 

 Taking to their boat, although the ship is much the safest, and 

 does not sink for a long time after being abandoned ; not con- 

 sidering, although the water gain on their pumps at first, they 

 may be able to hold away with it, when arisen to a certain easily worked 

 height in the hold ; because the velocity with which it will in a water- 

 enter, will be in proportion to the square root of the difference ^fch may** 

 between the level of water inside and out j added to this, the therefore, be 

 fuller the ship, the easier the pumps will work j therefore, i*"^ pt a * 

 they ought not to be so soon discouraged. 



V. 



Us if ul or Instructive Notions, respecting various objects. X.MuU 

 . tiplying of Copies of Writing. 2. Scintillation of the Stars, 

 3. Large Achromatic Lenses. — W. N. 



1 . Art of Copying, or of multiplying Copies. 



EVERY one is aware of the invaluable benefits which society 

 has derived from the arts of printing, by moveable types, as 

 well as by blocks and copper plates. But there are many cases, Benefits of the 

 in which it would be of advantage to produce copies of writing, art oi prUt- 

 without requiring a stock of types or engraved plates j and the 1 ** 

 presses, or implements, by which the impression is made. A 

 Vol. XXXIV.— No. 15;. I wving, 



