388 Rate of Going of two Clvcks. 



this city ; ,^mong others, those where Pytheas and Gassendi made 

 their famous observations of the solstice. These inquiries led us 

 to a careful discus?ion of their celebrated observations, and to the 

 discovery of another made by Pytheas at Marseilles, 350 years 

 before our aera, and which have hitherto been unknown. ' We 

 were only acquainted with, one of his for determining the sol- 

 stice, nienlionod by Strabo, to whom we are indebted for its 

 preservation. That which we have found, is the observation of 

 an equinox; which, according- as it is related by Hipparchus, 

 ought to have been made at Byzantium (the present Constantino- 

 plel, but we have proved by calculation that this observation 

 could only have been made at Marseilles; and we refer it to 

 Pytheas, to whom it undoubtedly belongs. These two observa- 

 tions, when properly computed, according to all the elements of 

 modern astronomy, have given us the true obliquity of the eclip- 

 tic at this remote period, and its diminution after a lapse of two 

 thousand years. The results agree with the theory in an ex- 

 traordinary manner." ' T. S. E. 



On the isochronous Rale of Going of tiuo Clocks under certain 

 Circumstances. By 5. A. DuLvc, Escj. F.R.S. 



To Mr. Tilloch. 



Sir, — I HAV'E found in 50ur number for last March, article 

 xxxi. a paper under the title of " On the Rate of Going of two 

 Clocks, with Remarks on Harris's Pendulum Clock, erected in 

 1814, by Mr. Thomas Reid." 



My present remarks shall be confined to the-following passages. 

 '^ The circumstance of two clocks keeping so closely together, 

 and for a period of considerable length of time^ appearing ex- 

 traordinary and unexpected to me, is the reason why I have 

 transmitted the case to you ; and should you deem it worthy an 

 insertion in your valuable journal, it is at your service. 



" Both the clocks were going in an imperfect state, and were 

 intended for further improvement ; but the assuming the ap- 

 pearance of keeping so near together, made me delay the taking 

 them down to make any alteration, till I saw how long they 

 would contiiuie to do so, which they did for such a length of 

 time, and might have done so for hoiv long, I do not pretend 

 to say, had it not at last become necessary for me to put an end 

 to it." 



I have seen a similar coincidence, the cause of which was at 

 last discovered. There were two clocks in a clock-maker's shop, 

 one of which was his time-keeper, and an excellent instrument ; 

 the other, which was intended to be regulated by the former, did 

 not agree when it stood at a distance : he then placed it close to 



the 



