TRANSACTIONS OF SECTION E. 815 



7. So7ne Notes on a New Method for the Determination of Oeographiral 

 Longitudes by Lunar Distances. By Dr. H. Schlichteb. 



Lunar distances as a means for the strictly accurate determination of geo- 

 graphical longitudes have been little used of late, partly on account of the 

 splendid chronometers with which ships are now provided, and partly owing to 

 the inaccuracies of the instruments commonly employed for lunars. For exploring 

 expeditions on land, however, chrouometers are of little value, and the other 

 astronomical phenomena which may be used besides lunar distances are either too 

 difficult of accurate observation by the majority of travellers, or occur too seldom, 

 or are not accurate enough. 



The author therefore introduces a new method of observation and measurement 

 of lunar distances, viz., by obtaining a parallel series of photographs of the moon 

 and a fixed star or planet on one plate, and afterwards measuring the distances on 

 the plate. For the elimination of all possible inaccuracies of the photographic 

 film or of the lens, the lunar distances thus registered are checked by repeatedly 

 photographing on the same plate two fixed stars, the positions of which are given 

 in the ' Nautical Almanac,' and the angular distance of which can easily be com- 

 puted therefrom. The angular distances of the photographic lunars are then found 

 by a simple proportion. The time for taking a set of eight photographic lunars on 

 one plate does not exceed three to four minutes, and micrometric measurements' 

 show with perfect accuracy the change of the lunar distances (owing to the move- 

 ment of the moon) during each interval of the eight observations. The minute 

 accuracy of the method is hereby established. The micrometric measurements on 

 the plate are made by means of the same ' rcseau' which is employed by the 

 principal observatories for stellar photography, and the measurements may there- 

 fore be regarded as absolutely correct. Results thus obtained give the correct 

 longitude of the place of observation. 



The author proposes to use this method for scientific expeditions into the 

 interior of continents, &c., as well as for the further determination and correction 

 of secondary meridians in navigation. For both purposes it is especially adapted 

 on account of its minute accuracy and great simplicity. 



[The paper will be published in the 'Proceedings of tlie R.G.S.'] 



SA TUB DA Y, A UG VST 6. 

 The Section did not meet. 



MONDAY, AUGUST 8. 

 The following Papers and Eeports were read : — 



1. Notes on a Portion of the Kalahari. By E. Wilkinson. 



These notes, which are accompanied by a map, deal with that portion of the 

 Kalahari lying north of a line between Kuis and Honing A'ley. The author i.-< 

 inclined to doubt the accuracy of the position of Kuis as given in previous map?, 

 and the location, if not the existence, of the fork of the Molopo Ki-\er which is re- 

 presented in them. The soil of the district appears to be a heavy loose sand, 

 which supports, nevertheless, an abundance of coarse grass, and is densely studded, 

 rather than covered, with low timber and bush. In the few places where water 

 is obtainable, the cattle look well, but the scarcity of water is the curse of the 

 district, and the natives say that it will pass the wit even of white men to find it 

 there. A great portion of the notes is taken up with this question of water 



