548 Mr. Hartnup on testing Chronometers [Dec. 14, 



of season and of geographical position, and also to point out the cause 

 of certain peculiarities in the climate of High Asia. 



As it has been ascertained that the paper was read to the Academy of 

 Sciences at Berlin on the 1st of June, and is printed at length, with its 

 accompanying plates, in the ' Monatsbericht ' for August 1865, the reader 

 is referred to that publication. 



II. " On testing Chronometers for the Mercantile Marine." By 

 JOHN HARTNUP, F.R.A.S., Director of the Liverpool Ob- 

 servatory. Communicated by the President. Received No- 

 vember 22, 1865. 



The late Admiral Beechey, on looking over the records of the Liverpool 

 Observatory in 1854, was strongly impressed with the importance of some 

 systematic plan being adopted for testing the chronometers employed in 

 the Mercantile Marine. He consulted many persons on the subject who 

 were interested in the security of navigation, but the difficulty which pre- 

 sented itself at that time was the long period required for the test, five or 

 six months at least being supposed to be necessary. 



About four years ago the Mersey Docks and Harbour Board gave me 

 permission to have constructed, for the purpose of testing chronometers, a 

 hot-air apparatus on a more convenient principle, and on a much larger 

 scale, than the one which I had heretofore employed ; and the arrange- 

 ments are now so perfect that chronometers can be tested efficiently in 

 five weeks. It appears that chronometers in the Merchant service, when 

 at sea, are generally exposed to temperatures ranging from about 55 to 

 85 of Fahrenheit, and that for most practical purposes it is sufficient for 

 the shipmaster to know the rate in the three definite temperatures 55, 70, 

 and 85. The following examples, taken from our records, will illustrate 

 the method I have devised to supply this information. The temperature 

 is changed 15 on Saturday mornings. No comparisons being made on 

 Sundays, the rate for Monday in each week is the mean of two days. 



TABLE I. Showing the daily rates, gaining, of six chronometers for five 

 weeks ending February 21. 



Mean 



No. i. No. 2. No. 3. No. 4. No. 5. No. 6. daily 



temp. 



8 S S S S S 



January 



Means 0'67 ... 0'75 ... 3'52 ... 3'02 ... T20 ... 2'55 ... 55 



