ISS Description of the Mooring Blocks 



as other eye-tubes, and is adjusted to distinct vision by the same 

 pinion motion. 



For the lowest magnifying power, the whole of the tubes must 

 be shut up ; and when tlie magnifying power is to be increased, 

 the smallest of the sliding tubes, A, nmst lie drawn out to either 

 of the numbers engraved upon it ; care being taken not to draw 

 out any part of the other sliding tubes, B and C, until the whole 

 of the first, A, is pulled out ; the second tube, B, may then be 

 drawn out to either of the numbers engraved thereon ; and in 

 like manner the third tube. The numbers denote the magni- 

 fying power of the telescope. 



To change the power, for any less power than the one to 

 which the tubes have been drawn out, the reverse of the above 

 described mode of proceeding must be observed ; and the largest 

 tube must be returned first, and so on, until they have been 

 brought back to the number required. Each alteration of the 

 magnifying power will require a new adjustment of tlie pinion; 

 and as the magnifying power is increased, the distance between 

 the eye-glass and the object-glass must be diminished. 



^*^ It is applicable to achromatic and Newtonian telescopes 

 of all lengths. 



XXX. Description of the Mooring Blocks now used in Ports- 

 mouth Harbour. By Mr. J. Park of Portsmouth*-. 



J Portsmouth-yard, March 25, 1818. 



Gentlemen, — A trust that the communication which I am 

 about to lay before you will not be deemed altogether undeserv- 

 ing your notice. 



In October 1705 I was appointed junior master attendant of 

 Portsmouth yard ; and as the security of his majesty's ships and 

 all works on float relative thereto are in the master attendant's 

 department exclusively, I applied myself as much as possible to 

 gain a thorough knowledge of the harbour, as well as of the na- 

 ture of the security and disposition of the moorings ; and the more 

 I became acquainted therewith, the less satisfied I was with the 

 method by which the ground-chain was secured, as a national 

 evil attended it, and various other inconveniences to the pubhc 

 service. 



The evil alluded to was that of throwing some thousand tons 



* From the Transactions of the Society for the Encouragement of Arts, 

 Manufactures, and Commerce, vol. xxxvi. The gold medal of the Society 

 was presented to Mr. Park for this great improvement respecting harbours 

 for king's ships ; and a model of the contrivance is preserved in the So- 

 ciety's Repository. 



of 



