919 



last tooth of the deciduous series. Thus determined, the homo- 

 logies of the other grinders are ascertained by counting the molars 

 from the first backwards, 1, 2, 3 ; and the premolars from the last 

 forwards, 4, 3, 2, I. The S3'mbols are made by adding the initial ??i 

 to the numbers of the molar teeth, and the initial/) to those of the 

 premolar teeth. The author concludes by pointing out the advan- 

 tages of this system of anatomical notation. 



2. " Description of the Hydrostatic Log." By the Rev. E. L. 

 Berthon, M.A, CommAU]icated by Sir Francis Beaufort, F.R.S. 

 &c., on the part of the Lords Commissioners of the Admiralty. 



The object of this invention is to obtain a register of the- speed 

 of ships, by a column of mercury, in such a manner that the height 

 of the column shall depend upon the velocity alone, and not be 

 affected by any disturbing causes, such as alteration of draught of 

 water, pitching and rolling, &:c. 



The principle embraces that of Pitot's tube, inasmuch as the 

 force of the resistance due to the velocity is communicated through 

 a small pipe projecting into the water below the bottom of the ship : 

 this force, acting upwards, compresses a portion of enclosed air in a 

 small cylinder, which air communicating by means of a little pipe 

 with the bulb of a glass tube — bent like a common barometer — 

 raises the mercury in the tube, by depressing it in the bulb. 



But as any single column of water and air thus acting upon the 

 surface of the mercury in the bulb alone must depend not only upon 

 the resistance due to the velocity, but also upon the distance of the 

 cylinder from the icater-Une, which distance or height varies with 

 every sea, and alters more permanently as the draught of water 

 changes, a compensation was necessary ; and the inventor has found 

 one, which he considers perfect for all these variations, by applying 

 a second column of water and. air to press upon the other surface of 

 the mercury, viz. that in the glass tube. This second column is 

 precisely like the first as regards the pipe and cylinder, and commu- 

 nicates with the sea by an aperture or apertures, presented in such 

 a direction that velocity does not produce any increase of pressure. 

 Thus the mercury in the indicator is placed between two columns 

 of water and air, which are always equal to each other in length, and 

 the mercury rises according to the difference between the pressures 

 upon its two surfaces, the result of resistance or velocity alone. 



The air-pipes may be conducted in any direction, and the indi- 

 cator, which swings upon gimbals, may be placed in any part of 

 the ship. The two water-pipes are conducted into one tube in the 

 bottom of the ship, divided into two separate chambers for the dif- 

 ferent forces. 



In addition to the speed, the true course or leeway of the vessel 

 is indicated upon a horizontal segment divided into degrees, over 

 which a needle is moved by a rod connected with the above-men- 

 tioned double tube ; and the whole is kept continually in the true 

 direction of the ship's motion by a float or vane attached to the 

 lower end of the tube in the water. 



