163 Miscellaneous InteUigeme. 



and the repetition of this operation produces great injury, in ad- 

 dition to that done by inking. To prevent this, Dr. M. proposes to 

 varnish the plate when laid aside, either with common lac varnish, 

 which may be removed, when requisite, by spirit of wine, or with 

 caoutchouc varnish. — Edin. Jour. Scien.i. 76. 



13. Impermeability of Glass to Water. — It has sometimes, though 

 not often, we believe, been suggested, that glass and siliceous 

 minerals are permeable to water. The Rev. Blr. Campbell, in a 

 voyage to South Africa, sent two globular bottles, hermetically 

 sealed, to a depth of 1200 feet in the sea, by two leads, one of 

 221b., and the other of 28lb. When the rope was brought up by 

 the exertion of ten men for a quarter of an hour, both vessels 

 were found empty. 



14. On obtaining the rate of Chronometers on Ship-board. 



To the Editor of the Quarterly Journal. 

 Sir, 



In Number XVIII. of the Astronomical and Nautical Col- 

 lections, you have inserted an excellent proposal of Mr. Fallows, 

 for regulating the chronometers of ships by the extinction of a 

 light at the place of observation on shore. 



A similar, and (as more extensively useful), perhaps, a better 

 plan of effecting that purpose, was laid before the Admiralty 

 fourteen years ago. The suggestion, however, was not adopted; 

 but, if it were to meet with your support, and that the Board of 

 Longitude were to recommend it to the present Admiralty, there 

 is little doubt that it would be carried into execution, and still 

 less that it would be attendee], with manifest advantage to His 

 ]\lajesty's service, as well as to all those India or other merchant 

 ships who carry chronometers. 



It is well known that the rate which a chronometer acquires 

 when on-board of a ship always differs from that Avhich it had 

 obtained while on-shore. Hence the propriety of ascertaining 

 the rate after it is placed in the situation it is finally to occupy ; 

 added to which, the obvious inconvenience of removal in bad 

 weather, the risk of boats, the frequent carelessness of those em- 

 ployed, and many other circumstances concur in proving that a 

 chronometer should not be disturbed if it is possible to fix its rate 

 in situ. 



With these views it was proposed, that at the Observatory, in 

 Portsmouth Dock-yard, a flag-staff should be erected; that 

 every day at a few minutes before some certain hour, a light 

 opaque ball (such as is commonly used for distant signals at sea, 

 and which would be visible to all the ships at Spithead,) should 

 be hoisted ; and that, at the precise moment agreed upon, the 

 ball should be hauled down. Two balls, one under the other, 

 and in close contact, would be still better, as their separation, by 



