306 SURVEY OF THE COAST 



time by the chronometer or clock, without taking the ob- 

 server away from the azinmth, then the above second ob- 

 servation of tiie terrestrial object in the reversed position of 

 the transit can be followed immediately by one of the sun 

 in the same position of the transit ; and returning the teles- 

 cope to the direct position, one can egain be niade in this 

 position, and the terrestrial object observed again for veritica- 

 tion's sake, the terrestrial observation in the reversed situ- 

 ation serving for both azinmths in that position. Thus lour 

 azimuths, each from six transits of the sun's limb at the ver- 

 tical wires, can be observed in a very short space of time. 



It is evident that these azimuth observations would, when- 

 ever found necessary, be very well suited for the reduction 

 to the mean time, according to the method invented by Mr. 

 Soldner. 



It is proper to make the azimuths as independent of the 

 rate of the timepiece as possible, and therefore to make ob- 

 servations of time as nearly as possible before and after tliose 

 of the azimuths ; and if several observers should be togetiier, 

 a proper combination, which would admit both observations 

 to be made at the same time, would be very advantaj;eous. 



The calculation of the result can of course be varied ; be- 

 ing made either for each limb's transit, or, as I did, for each 

 transit of the centre ; but it is not allowed to take direct and 

 reversed observations together in the same calculation. 



The form of such an observation, and the manner of re- 

 gistering the results, will be seen in the corresponding ex- 

 amples of the Day -Book and Journal of Results. 



I will here describe another metliod of ol)serving azimuths, 

 which may be of use in circumstances which admit only a 

 portal)le transit and the means of determining the time. I 

 applied it in 1793 in Switzerland, and it may sometimes be 

 preferable to a measurement on a less accurate instrument. 

 I adjust the transit telescope exactly in the vertical of the 

 object, before the time when the sun will pass this vertical, 

 and observing the transit of l)oth limbs on all the wires, tlie 

 time of the transit of the centre is thus obtained ; and it is 



