Vertical Component or Magnetic Force. 



373 



Note on the least probable error of an observation of the horizontal component of magnetic force. — 

 Investigations for the probable errors of observation corresponding to those for the magnetic declination, have 

 not been made for the horizontal component ; it will not be difficult, however, to approximate to the least 

 probable errors of an observation from the values of the mean difference. The mean difference of an 

 observation is least in the month of January, and in the months of June and July, being 0-00035, 000040, 

 and 0-00047, for the three months respectively ; which, if the distribution of the errors follows nearly the same 

 law as that found for the magnetic declination, will give probable errors of about 0-00024, 0-00027, and 

 0-00032, of the horizontal component. 



The mean difference, for the year, of an observation of the horizontal component, is a minimum about 

 6 h a.m., and l h and 2 h p.m., being about 0-00050 ; the probable error is about 0-00034. 



In order that an observation of the horizontal component should have the least probable error, it should 

 be made in the months of January, June, or July — and early in the morning. The least probable errors are 

 about 2 h a.m. in these three months, being less than two ten-thousandths of the whole horizontal component. 



Vertical Component of Magnetic Force. 



TABLE XXXVIII. — Mean Values of the Variations of the Vertical Component of Magnetic Force, the 

 whole Vertical Component being Unity, for each Civil Week-Day, Week, and Month of 1844. 



Civil. 

 Day. 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 





o-no 



0-00 



0-00 



(win 



0-00 



0-00 



0-00 



0-00 



0-00 



(>•(!() 



0-00 



0-00 



1 



7994 



7784 



7531 



7351 



7065 



6888 



6572 



6402 



[6297] 



6027 



6031 



[6084] 



2 



8014 



7709 



7277 



7214 



7156 



[6976] 



6664 



6269 



6386 



6448 



6015 



6092 



3 



7945 



7521 



[7299] 



7191 



7129 



7044 



6617 



6208 



6315 



6331 



[6046] 



6057 



4 



7907 



[7646] 



7178 



7415 



7392 



6993 



6668 



[6357] 



6353 



6322 



6054 



6087 



5 



7850 



7691 



7264 



7408 



[7215] 



7030 



6657 



6344 



6295 



6330 



6054 



5897 



6 



7877 



7587 



7186 



7108 



7222 



6978 



6634 



6445 



6389 



[6303] 



6134 



5996 



7 



[7896] 



7582 



7292 



[7343] 



7267 



6986 



[6682] 



6476 



6274 



6293 



6238 



5980 



8 



7912 



7661 



7189 



7456 



7123 



6916 



6782 



6510 



[6320] 



6271 



6138 



[5940] 



9 



7917 



7501 



7433 



7325 



6981 



[6921] 



6672 



6615 



6410 



6269 



6081 



5945 



10 



7916 



7534 



[7413] 



7348 



7267 



6861 



6678 



6298 



6230 



6150 



[6173] 



5924 



11 



7893 



[7509] 



7450 



7397 



7349 



6893 



6637 



[6386] 



6321 



6141 



6161 



5896 



12 



7887 



7521 



7603 



7438 



[7104] 



6893 



6577 



6279 



6282 



6159 



6233 



5856 



13 



7913 



7458 



7509 



7409 



7174 



6791 



6636 



6253 



6294 



[6119] 



6186 



5875 



14 



[7893] 



7378 



7524 



[7447] 



7087 



6894 



[6607] 



6360 



6328 



6086 



6106 



6167 



15 



7900 



7219 



7491 



7254 



6767 



7014 



6684 



6349 



[6248] 



6097 



6172 



[6001] 



16 



7893 



7314 



7555 



7284 



7107 



[6872] 



6610 



6352 



6178 



6083 



6761 



6124 



17 



7873 



7226 



[7440] 



7901 



7133 



6768 



6499 



6353 



6136 



6143 



[6311] 



6037 



18 



7853 



[7282] 



7392 



7359 



7222 



6831 



6491 



[6327] 



6271 



6186 



6280 



5947 



19 



7718 



7261 



7360 



7485 



[7076] 



6935 



6567 



6370 



6306 



6225 



6288 



5932 



20 



7800 



7334 



7318 



7453 



7047 



6936 



6527 



6263 



6096 



[6079] 



6262 



6050 



21 



[7803] 



7338 



7300 



[7394] 



6989 



6893 



[6510] 



6278 



6412 



5684 



6173 



6009 



22 



7850 



7357 



7398 



7395 



6961 



6862 



6477 



6453 



[6249] 



6059 



6209 



[5972] 



23 



7776 



7419 



7391 



7399 



6605 



[6771] 



6479 



6492 



6337 



6176 



5971 



5969 



24 



7824 



7379 



[7378] 



7273 



7094 



6744 



6519 



6253 



6211 



6060 



[6093] 



5931 



25 



7585 



[7414] 



7395 



7424 



6949 



6628 



6502 



[6341] 



6130 



6096 



6052 



5942 



26 



7709 



7420 



7348 



7400 



[6888] 



6564 



6408 



6287 



5955 



5804 



6074 



5949 



27 





7414 



7434 



7160 



6843 



6601 



6487 



6299 



6355 



[6002] 



6077 



5887 



28 



[7654] 



7496 



7390 



[7313] 



6890 



6627 



[6375] 



6263 



6138 



5975 



6082 



5993 



29 



7690 



7358 



7290 



7466 



6947 



6615 



6324 



6288 



[6198] 



6019 



6080 



[6094] 



30 



7661 





6360 



7362 



6922 



[6616] 



6323 



6211 



6264 



6059 



6109 



6326 



31 



7623 





[7183] 





6980 





6204 



6229 





5986 





6206 



Mean 



7838 



7458 



7341 



7384 



7062 



6847 



6552 



6341 



6267 



6129 



6155 



6003 



Table XXXVIII. has been formed from the daily means in micrometer divisions by the following formula : — 



f=n 0-00001, 

 where / is the quantity in the Table, and n is the daily mean in micrometer divisions corrected for temperature. 



MAG. AND MET. OBS. 1844. 5 B 



