C—la

34

To simplify matters the corrections can be put in tabular form. Example from F.B. 34, p. 19. Mean error in run for mic. B . . .. — 0>62" Mean run for mic. A .. .. .. .. = 2*30 Sum .. .. .. .. .. = 2-92 Total mean run .. .. .. .. = 1 -46 Extreme correction = half run . . . . = 0-73 This 0-73" is distributed over two and a half revolutions of the micrometer screw-head = 150", since when the zero-line comes at mid-interval there is 0 correction. 150 A change of 0-1" of run-correction is equal to _,o = 20-5" of the screw-head reading.

Table.

Working from 2' 30", adding and subtracting half 205" gives figures 2' 40-2" and 2' 19-8"; and from these figures, adding and subtracting the full 20-5" gives the remainder of the figures for the table. Since the / readings are less than the b readings, the sign is + from 2' 30" to 5' 00", and — from 2' 30" to o'. In using the table it is not necessary to correct every individual reading, but the figures may be grouped into sets of face left and right readings, and the corrections applied to the means. Taking the first four columns F.B. 34, page 19, and grouping the face left and right readings, gives the following results : —

Limits for 0-1 Runcorrection. Run-correction. Limits for O'l Runcorrection. ! 0' 16-8" - -7" + 4' 43-2" -■6 + 4 22-7 0 37-3 - -5 + 0 57-8 4 02-2 1 18-3 -•4 + 3 41-7 1 38-8 -■3 + 3 21-2 ] 59-3 -•2 + 3 00-7 2 19-8 ... ,] + 2 40-2 - ■() -f 2 30-0 2 30-0

Mark. j Face. Mie. b. /• b-f=r. Mean '< + / 2 Runcorrection. Corrected Means. I Brooklyn L i E( B A B A 360° 00' 07" 02 11 11 [08 L 00 Bio tJ0 360 00 07-0 Wadestown •{ A B A 360 00 07-7 203 15 10 09 17 12 07-0 08 06 17 Id 0-7 7-3 -0-7 Belmont B A B A 203 15 12-0 218 30 26 30 34 30 10-2 26 28 31 27 1-8 11-1. -0-7 203 15 10-4 E( 218 30 30-0 28-7 1-3 29-3 - 0-6 218 30 28-7 Somes B A B A 251 44 30 33 36 30 30 31 35 27 M El 251 44 32-0 251 44 32-2 30-7 1-5 31-4 + 0-6