31

C—lα

Table No. 5.—Comparison of Half-chain Lengths.

Observations for the Probable Error in laying down a Comparator. Imperial Standard Steel Reference Tape is standard at 62° Temperature bvjthermometer N0.'263 = 59° H „ N0.'264 =59 Mean temperature .. .. .. 59 Difference .. .. .. .. 3° Coefficient of expansion adopted = 0-00000625, which multiplied by 3 = 0-001875 link ; and the true length of comparator = 100-0000 - 0-0019 = 99-9981 links. Continued comparisons of same, steel reference tape with the above comparator value 99-9981, each comparison being carried out in the same manner as if a new comparator was being established :— First Set. J. Langmuir reading scale ; H. M. Kensington making contact, rear end. Note.—Perfect open-air conditions taken as 7 ; then the conditions for observations Nos. 1 to 5 will lie 5. Deg. Fahr. 1. (a.) Tape is long = 4- -0003 Thermometer 263 at 59-1 264 „ 59-0 (6.) „ =4- -0001 „ 263 „ 59-1 264 „ 59-0 Means .. 4- -0002 Thermometer at 59-05 2. (a.) Tape is long = 4- -0002 Thermometer 263 at 59-1 264 „ 59 (b.) = + -0002 „ 263 „ 59 264 „ 59 Means = 4- -0002 Thermometer at 59-025 3. (a.) Tape is long = 4- -0014 Thermometer 263 at 60-1 264 „ 60-0 (b.) = + -0015 „ 263 .. 60-1 264 „ 60-1 Means .. 4- -00145 Thermometer at 60-075 4. (a.) Tape is long = + -0009 Thermometer 263 at 60 264 „ 60 (b.) = + -0009 „ 263 ~ 59-5 264 „ 60-1 Means .. 4- -0009 Thermometer at 59-90 5. (a.) Tape is long = 4- -0013 Thermometer 263 at 59-8 264 ~ 60.1 (b.) „ =4- 001 I ~ 263 „ 60-0 264 „ 60-1 Means = 4- -00135 Thermometer at 60-0

t in. Invar 7 Tape No. OS. A end, Ii nice. i', Name of Hali-ehain. Difference in Length. True Value of 100 Links. True alue of each j Difference from Half chain. 50 Links. 0-50 links il-lOO „ •0 + 0037 99-9932 49-9947 - -0053 (| 49-9985 --0017)