Re cpir 
@ basis 0} gs in 
hag. aa Ra be determined hereafter whale the marks have 
~ the star, similarly for the two circles for the other star. 
130 NEW METHOD OF DETERMINING TRUE NORTH OR SOUTH. 
The more frequently the true south. or oath is referred to as 
in the survey of land, the better will the 
pias Re i and the more accurate will be the maps of the 
isi ‘writing the above I have adapted this method to a smaller 
telescope of 9-1 inch focal length, which is the ordinary size fora — 
5-inch theodolite. On a bright moonlight night, and with the — 
lines illuminated, the stars can just be seen distinctly enough for — 
observation. Very satisfactory results were obtained, and if the 
lines and circles are well drawn on the glass I estimate the maximum 
error of the method at about 15 seconds, The cost of shes ; 
the glass diaphragm instead of the spider-threads will be ' 
10s, ; the former serving also for field use may be permanently — 
telescope which I thought at first necessary is now dispensed with — 
I may mention that for the small telescope the lines on the — 
glass should not Ee aut too fine, as moderately thick ones are seeh — 
with less illumina 3 
It will be eed that the stars above mentioned are only visible j 
in the southern hemisphere, but a and A Urse m minoris may be — 
similarly observed in the northern hemisphere. These two are 
suitable for small instruments, whilst for larger, other suitable 
stars nearer the pole may be selected. 
For computing the sizes of the circles :—Linear radius of circle 
= focal length x tan. required angle, the angle for one circle being 
slightly over and for the next circle slightly under the N.P.D. of 
I desire to express my thanks to Mr. H. O. Russell for his 
— and help in working out the details of the mechanisii. : 
