46 HYDROORAPHICAL SURVEYING [chap, i 



All such are now supplied by the Hydrographic Office, and 

 it is not necessary to specify them. They are all enumerated 

 in the Instructions to Surveyers. It is very necessary to 

 record observations in these books in such form that they can 

 be hereafter consulted as records. 



CHRONOMETERS. 



About the care of the chronometers little need be said. 

 Full instructions are issued by the Admiralty on the subject, 

 to which reference can be made, and Captain Shadwell's 

 " Notes on Management of Chronometers "* contains all that 

 can be said on the subject. The box or " room " for the 

 chronometers is now made after a fixed plan, the principle of 

 which may be said to be that the solid block on which the 

 chronometers rest, and which is, when practicable, bolted to 

 the beams beneath, not the deck, can receive no blow or 

 shock other than those communicated through the ship her- 

 self, which is done by surrounding it with a bulkhead, with a 

 clear space between. Vibrations are lessened as much as 

 possible by the interposition of sheets of india-rubber in 

 building up the block, and by padding the partitions in which 

 each chronometer rests \vith soft cushions. 



The lid of each box is removed, and a general lid covers, 

 the whole. 

 Uni- A sheet of fearnought is laid over the chronometers, and has 



Tem^era°^ flaps cut over each one, so that they can be uncovered in turn, 

 ture. for purposes of comparison or winding. This is to assist to 

 keep the temperature uniform, and also deaden the ticking of 

 other watches when comparing. 

 Winding. Winding is performed at the same hour daily, and com- 

 paring also. There is no necessity that these hours should be 

 identical ; but it is generally the practice that they should be. 

 If they are both done at an early hour, there is more chance 

 of the same officer being on board to do it, which is of im- 

 portance. 



Always wind until the mechanism is felt to butt, to ensure 

 the watch being fully wound up. 



■■' " Notes on Management of Chronometers and Measurement of Meridian 

 Distances," by Captain C. Shadwell, C.B. Potter, London, 1861. 



