454 CANADIAN LONGITUDES. 



signal at 4h. 30m. 10s., if no time is lost, B will receive the signal at 

 4li. 50m. 10s. ; but as we suppose the signal to occupy one second in 

 passing from A to B, B will receive the signal at 4h. 50m. lis., and 

 the difPerence of meridians will be 20m. lOs., a second too much. 

 But supposing B to send a signal to A at 4h. 50m. 10s., then A will 

 receive it at 4h. 50m. lis., and the difference of time will be 19m. 

 59s., evidently one second too little, but the mean of the results give 

 20m., the correct difference of longitude. Therefore by the observers 

 exchanging places, and by sending the signal backward and forward, 

 the greatest accuracy may be obtained. 



Lunar and Stellar photography may be the means of superseding 

 the laborious and imperfect manner of taking observations with the 

 human eye ; and it is to be hoped that the noble example set by the 

 Observatory, Cambridge, U. S., in this respect, may be followed by 

 others, and that we shall ultimately succeed in making the heavenly 

 bodies register their own observations. With respect to Stellar pho- 

 tography, so much will depend upon the state and purity of the 

 atmosphere, that but few places are well adapted to this mode of 

 observing, but many say that Quebec has the advantage in this respect 

 over most other places in British America, and I sincerely hope that 

 ere long Stellar photography will be taken up by Canada. 



Before giving my report on the determination of longitude, I will 

 make a few observations, that may be useful to those who may be 

 occupied on a future occasion in determining meridional distances. 



On arriving at the place, just call at the telegraph office and make 

 friends with the department, as without their hearty co-operation it is 

 useless to proceed. Then look out for some rocky ground near to the 

 office, where you can build your observatory. Let the support of 

 your instrument be of stone, and of a height that will enable you to 

 apply and read the level when standing on the ground. This is of 

 great importance, as the level must be applied quickly and often. 

 Also take care to have the screw that moves the instrument in azimuth 

 to your right hand, in looking to the northward. If you are left- 

 handed, vice-versa. See that the Collimation has not been thrown 

 much out by travelling. If it has, correct it as nearly as you can 

 by the middle wire in reversed positions. 



As you do not know the longitude of the place within two minutes, 

 and as the rate of your chronometer should not be trusted with its 

 former rate, after travelling, you can not get the instrument into the 



