186 PROCEEDINGS OF SECTION A. 
ACCURACY, AS COMPARED WITH OTHER SURVEYS. 
The errors of close of the triangles will be found on the accom- 
panying map (Map A), and comparison of the errors with those 
met in other surveys shows the work done here to be of a very 
high degree of precision. The writer had an opportunity in 
August, 1893, of making a comparison of the relative accuracy 
of this and other surveys, principally those of Europe. Thanks 
to valuable information received from Dr. Helmert, President of 
the International Geodetic Association, it was possible to present 
this in a very complete form, and though it was published as an 
appendix to the departmental report of the work of the year 
named, yet the results may not be without interest in this paper, 
and it is therefore reproduced in part, some further information 
being added from a similar comparison made by Dr. Gill and 
published by him in 1896. 
As a means of comparison, the criterion has been adhered to 
which is now of general use, viz., General Ferrero’s “m,” which 
may be taken as representing with close approximation the mean 
error (as deduced from the closing errors of the various triangles 
of each system) of the angles used in the sur vey. This quantity 
is computed by the formula— 
m= — 
in which A is the closing error of the triangle and 72 the number 
of triangles dealt with. 
The following are the values of m :— 
m. 
“ 
Austro-Hungary, 1849-88, 674 triangles ........... cesses sereenens + 0°931 
Bavaria, 1801-54, 337 a I Pl marsitenae tenn ee a, ea act aa + 1:'800 
Belgium, 1851-73, 219 EN 1 Vala See NAS ae va ane + 0:890 
Denmark, eUires 20 poet —eteBs toutes. chwocten wee naan + 0°788 
cs 1837-47, 43 PRM ern eee moe eadacn Sarcoc + 0°893 
SGT SAOS. MGs Beat srease kgscenes otoceodotoaaee + 0°442 
France, old meridian series from Dunkirk to Fontainebleau and 
Bourges, L792=1827, 10d triangles eeeece-vereecescr ee rrsece + 1:080 
France, triangulation wv the parallels, 1804-27, 478 triangles + 1:900 
39 “s connecting England, 1863,  §& 53 .» a O10 
», new meridian series, 1870-88, 119 triangles ............... + 0°560 
Algerianand Tunis, since 1860, 140 ee EN ee Ty + 0°830 
Great Britain, 1792-1852, 476 triangles aaa aac 2 01s ee Meee + 1:790 
India, Dehra Dun, 80 triangles SHERROD tocaido ve attain deo lost stiontedenine + 0°780 
», Gurhagarh meridian senles VOSttriangles) Sa-c.ccnscereeeeeeee + 0:930 
»» Singi and Khaupisura meridian series, 101 triangles ...... + 1:215 
ditalysli850=885 507i triangles acmacccnteeeees er ocaneeeer eee aeeeneeaeee + 0:940 
Mecklenberg, 1854-60; 69 triangles 22.2. cmacccceeesnreucsecseeeeeeereee Se leisy 
Norway, 1862-88 (nnmber of triangles unknown)......... dane cnn + 0°720 
Portugal, 856-88, 139) triangles ..)sascusce auearsdncoeeaentnsesastarent == 1126 
Prussia, land survey of Prussia, G38ttrianGles My ecccasceec cates + 0°567 
NG East Prussian degree measurement, 29 triangles ........ + 0°688 
