229 



ducing energy may be attained by a moderate increase of the size of 

 the syringe. 



The amount of other consumed in an observation rarely exceeds 

 half a dram, and frequently falls a good deal short of this, the cost 

 thus being from a halfpenny to a farthing. The residual ether may 

 be repeatedly employed, making up its amount each time to three 

 drams from fresh ether. It ought to be kept for use in a separate 

 little bottle. The leather of the piston ought to be occasionally 

 rubbed with olive oil, and the washers of tho connecting screws ought 

 not to be allowed to become too dry. The syringe must be of the 

 most approved construction, and all the apertures of the neck of the 

 bottle and of the valve-piece sufficiently wide. Comparative obser- 

 vations have been made regarding the indications of this instrument, 

 of Daniell's hygrometer, and of Dalton's mode of transference of a 

 cold liquid from one vessel to another, which last is usually admitted 

 as a kind of standard of compression. Those of Daniell are usually 

 a very little in excess, and those of this instrument a very little in 

 deficiency ; but the deviation of both is on an average within 1° 

 Fahrenheit. 



The instrument is constructed by Messrs Kemp of Edinburgh, 

 with the proper accompaniments of measure, bottles for ether, &c., 

 all packed in a little box. It is thought that it will be found to 

 offer advantages in point of considerable security from accidental 

 fracture in travelling. 



2. On the Stability of the Instruments of the Royal Observa- 

 tory. Bj Professor Fiazzi Smyth. 



In an observatory where, as in that of the Calton Hill, the prin- 

 cipal object of pursuit is the determination of the exact places of the 

 fixed stars, and the investigation of those exceedingly slow secular 

 variations, which require many thousands of years to run their cycle, — 

 the stability of the instruments, as a necessary element to the accu- 

 racy of the observations, becomes of the extremest importance. 



To secure this quality much invention and no little ingenuity have 

 been employed, but not yet with perfect success ; for invariably the 

 more accuracy we demand, the more insuperable difficulties appear 

 to arise. Even nature at last appears to be taxed beyond her powers, 

 for we find when we have passed beyond a certain degree of magni- 

 fying power, that there are no bodies absolutely stiff and rigid — none 

 constuully of the same dimensions ; but all are expanding and con- 



