president's address. 31 



signal from Qreenwieh; and two under the sole control of 

 the Astronomer Eoyal are also dropped daily at 1 p.m., one 

 at the Eoyal Observatory and the second at Deal. The 

 dissemination of Greenwich time-signals has been the means 

 of adding considerably to the punctuality of railway trains, as 

 since the adoption of Greenwich time throughout the kingdom, 

 no excuse can be made on account of the difference of clocks. 



But if true Greenwich time is found to be essential in our 

 home life, how much more necessary it becomes to the seaman 

 when thousands of miles away from port. Let us see how the 

 astronomer comes to his assistance. Just look for one moment 

 into the chronometer room at the Eoyal Observatory. You 

 cannot avoid being attracted by a universal buzz, reminding you 

 of the hum of a beehive, for sometimes more than two hundred 

 chronometers are stored here at one time, all of which are rated 

 daily and kept ready for use in Her Majesty's ships when 

 required. It is pleasing to know that the commanders of our 

 noble ships may obtain one of these delicate chronometers, 

 preserved and rated daily by astronomical observations, by 

 which they are enabled to ascertain accurate Greenwich time 

 when at sea. Without this information and the predicted 

 positions of the sun, moon, and stars, given in the " Nautical 

 Almanac," and derived from the refined theories of the mathe- 

 matical astronomer, the seaman could never ascertain his true 

 longitude and latitude at sea, but would have to rely on the 

 primitive methods of navigation practised by the ancient 

 mariner. 



Astronomy is also employed in determining the figure of 

 our globe, and the relative positions of points on its surface. 

 By a comparison of the respective local clock-times found 

 directly from observations of selected stars at two distant 

 stations, the difference of longitude is at once found, and by 

 observing on the meridian the altitudes of stars whose declination 

 is accurately known, the latitude of any station can also be 

 determined. Longitudes may be obtained by several astron- 

 omical methods, but the easiest, and at the same the most 

 satisfactory, is by the observation of galvanic signals transmitted 

 from one station to the other, the local clock-times and signals 

 T?eing recorded automatically on a chronograph at both stations. 



