20 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



the chronometer is perfectly reliable an assurance that is 

 often fortified by very deceitful figures. The difficulty and 

 expense of a searching investigation into the errors to which 

 every chronometer is liable have long been supposed by the 

 trade to stand in the way of the introduction of such chro- 

 nometers only as were of approved reliability. In order to 

 obviate the difficulty as far as possible, the Liverpool Observ- 

 atory has been constructed by Mr. Hartnup specially for 

 the purpose of studying the rates of the chronometers that 

 may be sent thither by captains sailing from that port. The 

 expense of the examination given to such chronometers is 

 comparatively trifling ; and the number of chronometers sub- 

 mitted to him has annually increased, until, by reason of the 

 recent regulations at that port, the number of examinations 

 has amounted to between one and two thousand annuallv, 

 the same instruments having been repeatedly submitted to 

 him. The process pursued by Mr. Hartnup consists in ex- 

 posing each chronometer for a week to a uniform tempera- 

 ture of 55, an'd determining its rate each day; it is then for 

 another week exposed to a temperature of 70, and then to 

 one of 85 ; the next week it is returned to the temperature 

 of 70, and the last or fifth week it is exposed to the tem- 

 perature of 55, as at first. By means of general laws regu- 

 lating the rates of chronometers, it is now possible to deter- 

 mine what the rate will be at other temperatures than the 

 three above mentioned, and, knowing these, the navigator is 

 able to apply the proper correction to his time-keeper so ex- 

 actly that he need never mistake his position upon the ocean. 

 The records of the Liverpool Observatory for the past year 

 show 1. That the rates of about ten per cent, of chronome- 

 ters tested (those of the mercantile marine very generally 

 have the ordinary compensation balance) are so irregular as 

 to render the instruments entirely unfit for nautical purposes. 

 2. The error of adjustment for temperature of the remaining 

 ninety per cent, is often so erroneous as to produce a change 

 of daily rate of many seconc^s, when the temperature varies 

 but little from either of the two standard points of 55 and 

 85, or thereabouts. 3. That the best-made and most care- 

 fully adjusted instruments gain, on the average, daily six 

 tenths of a second more at a temperature of 70 than at 55 

 or 85. 4. That those that have the same rate at 55 and 



