362 A. D. Bache on a Magnetic Survey of Pennsylvania 
No. Station. Latitude. Longitude. yore y 
°] 
1 | Harrisburg, bo 27 76 88 3:97, 
2 | Huntingdo 4o 51 78:03 1:94 
3 | Near Pittsburg, 40°47 79° 0°20 
4 | Near Brownsville, 39°99 79°80 049 
5 | Near Mercersb 39°78 7793 097 
6 | Baltimore, 39:30 76°61 2°34 
7 | Philadelphia, 39°97 a5: 59 38 
8 aston, 40°70 75°25 36: 
9 | Williamsport, 41-23 77:03 3:54 
10 | Curwinsville, 40-96 78-60 177 
II : 41-23 80 27 -0'83 
12 rie, 42°13 80:10 2 
13 | Dunkirk, 42°49 79°38 0-90 
14 | Ellicottsville, 42°30 78:73 262 
15 ath, 42:35 77°35 355 
16 | Silver Lake, 41-94 6°03 452 
Mean, 40°98 77°95 2°08 
The small extent of the survey, as well as the comparatively 
small number of observations, will not permit the introduction 
straight lines. This assumption also serves for the recognin 
of = local disturbances as indicated by the differences of o 
served and computed values. 
Let 
D= + 2°08 + 2dL + ydM cos L, 
where 
di=lat. —40°-98 
dM= long. —77 °95. 
The 16 conditional equations have been formed and valu 
x, y and D found from the normal equations are as follows: 
a= +0:5102 Ke 
y= — 1:206 
D= + 2°-08-++-0-5102 dL — 1-206 dM cos L. 
A comparison of the observed and computed d ge 
shows ‘Ge icauty of introducing a term involving aLdM cos bi 
this has been done, and the solution of the normal equ@ 
gives us the following expression. : 
D=+2°14-10513 dL—1-231 dM cos L—0-203 dLdM eos be 
Comparison of observed and computed values. 
A Observed | Computed | Observed 
esa | Declination. | Declination. — Computed. 
y 36 
Harrisburg, 3°27 42°67 + 
Huntingdon, I° 182 +407 
Near Pittsburg, 0°20 o13 +04 
| Near Brownsville, 0-49 o16 | +420 
Near Mercersburg,| 0° 1°54 -34 
| Baltimore, 2 2°21 +08 
values 5 
eclinations 
