Reductions to Standard Instruments 49 



Dover circle 178. ^Type (a); the property of the Department. It was used in Mexico for a few 

 stations in 1906, by the Galilee during her cruises in 1906 to 1908, in Ecuador, Colombia, 

 and Central America, 1908 to 1909, in Canada in 1910, and on the Carnegie during her 

 first cruise in 1909 to 1910. For the Mexico work of 1906, the adopted corrections are: 

 for the mean of needles Nos. i and 2, i'.5 ; Nos. 5 and 6, i'.5. The corrections resulting 

 from a least square adjustment of the land intercomparisons of the Galilee work for use 

 during 1907 and 1908 are given by the formulae: 



Needle No. i FM = - i'.8 + 3'.! cos / - o'.2 sin / 

 Needle No. 2 FAI = i .7 + 2 .3 cos / + o .7 sin / 

 Mean, Nos. i and 2 FAI = i .7 + 2 .7 cos / + o .2 sin Z 

 Needle No. 5 FM = 3 .0 + 3 .4 cos J 

 Needle No. 6 FAI = i .4 + o .9 cos I 

 Mean, Nos. 5 and 6 FAI = 2 .2 + 2 .2 cos I 

 Upon the return of the instrument in June 1908, it was thoroughly overhauled. For the 

 South and Central American work of 1908 and 1909, the corrections adopted from a least 

 square adjustment of experimental and standard intercomparisons are given by the 

 formulae : 



+o'.2 + o'.4 cos / + o'.5 sin I 

 +0 .3 o .4 cos / o .1 sin / 

 +0 .3 .0 cos / + 0.2 sin 7 

 +0 .2 I .0 cos / + 0.3 sin 7 

 +0 .4 + I .2 cos 7 + o .3 sin 7 

 +0 .3 + 0.1 cos 7 + o .3 sin 7 

 During the cruise of the Carnegie the needles all developed rust traces and pits so that 

 very few available results were obtained, and the formulae for 1908 to 1909 had to be used. 

 The tabular designation is 178' 1256. 



During July to October 1910, while the defective pivots of the regular dip needles of 

 this circle were being renewed, some observations were made in Canada, using dip needles 

 Nos. 5 and 6, and intensity needles Nos. 7 and 8 of circle 206. The corrections adopted 

 for this work from intercomparisons with standard earth inductor are: needle No. 5 of 206, 

 I'.o; No. 6 of 206, 2'.o, and No. 7 of 206 deflected by No. 8, 3'.o. The tabular 

 designation is 178- (567). 



The adopted corrections of declinations observed with the compass attachment are: through 

 June 1910, +i'.2; subsequently, after repairs to compass, 3'.o. 

 Lloyd-Creak Dover circle i8g. Type {b) as modified; the property of the Department; has two 

 deflection distances and a telescope. It was used in the Pacific Ocean on the Galilee 

 from July 1907 to the completion of her work in 1908 and during the latter part of 1908 

 in the Guianas, South America. The correction for the Galilee work as deduced by least 

 square adjustments of the data from land intercomparisons are given by the formulae: 

 Needle No. 5 FAI = o'.j + i'.6 cos 7 2'.4 sin 7 

 Needle No. 6 FAI = i .1 + 2 .1 cos 7 i .2 sin 7 

 Mean, Nos. 5 and 6 FAI = o .9 + i .9 cos 7 i .8 sin 7 

 Needle No. 3 deflected by No. 4 at long distance, 



FAI = I .5 I .3 cos 7 0.2 sin 7 

 Needle No. 3 deflected by No. 4 at short distance, 



FAI = 3 .7 + I -3 cos 7 + 2 .4 sin 7 

 Before the work in the Guianas was taken up the blades of needles No. 5 and No. 6 were 

 polished so that only the formulae for needle No. 3 are used for that work; the corrections 

 as adopted for the range of dip covered are: needle No. 5, +10'. o; No. 6, o'.2; No. 9, 

 1'.5, and No. 10, o'. The tabular designation is i89'56 or i89-569-io. 



This circle has been in use on the Carnegie since the inauguration of her work chiefly 

 as an ocean instrument and but limited use for land work was made of it on the first cruise. 

 For the latter purpose, chief reliance was put on land dip circle 201. Since the first cruise 

 all land values obtained by the Carnegie are based on earth inductor No. 2 and land dip 

 circle No. 201. 



The correction adopted for the auxiliary land stations with 189 in 1909-10 was for 

 mean of needles Nos. 9 and 10, 2'. 8 for station near Falmouth, England, and 2'. 2 



*> 



'^ 



