642 MR. A. W. RUCKER AND DR. T. E. THORPE ON A :^[AGNETIC 
The directions of the Horizontal Disturbances are rather erratic, but they increase 
in inag'nitude as the r(>cks are approached. The (algebraically) small values of the 
Vertical Disturbing’ Iforce near to the northern edge of the basalt aie difficult to 
explain as the results ot induction, in view of the gradual slope ot the mass of tiap 
shown in the section of the hill close to our stations, published by the Geological 
Survey of Ireland (Horizontal Section, Sheet /, Section 2). 
If the rock is permanently magnetized, the result could be more easily accounted 
for. Whether, owing to this cause, or to variations in permeability which make the 
effcicts irregular, our experience is that, while the attraction exerted by very large 
masses of basalt (such as that ni A-iitrim) can be demonstrated at places neai to but 
not actually on the magnetic rock, yet on the surface of the basalt itselt repulsive 
forces are at least as common as attractions. 
This is certainly true of Antrim, and is suggested by the experiments at Kilteely. 
The whole question as to the cause of the permanent magnetism of rocks is 
obscure, but there seems little doubt that, while it plays a great part in producing 
local disturbances, it is so irregular that it gives rise to no regional effects. 
Observations were made at another set of live stations near Cromivells Hill, about 
two miles south of Kilteely. This spot was chosen because the section published by 
the Geological Survey runs through the hill. It is a mass of elvauite, about half a 
mile long by 300 yards wide. There wms, therefore, every reason to expect that 
the Disturbances would be less than at Kilteely. 
The results were as follows, in terms of O'OOOOl C.G S. unit. 
Cromwell’s Hill. 
1 
No. 
- 
Description of station. 
Components of Disturbing Force. 
N orth. 
West. 
Vertical. 
7.57 
500 jai'ds S. of tbe kill . 
+ 89 
_ 5 
4- .59 
756 
100 vards S. of the hill. 
+ 44 
-32 
+ 1 
755 
Close to the S. edge of the igneous rock . . 
+ 25 
-60 
— 36 
758 
About 100 yards N. of the igneous rock, but 
+ 36 
759 
dne W. of the centre of the mass .... 
400 yards W. of the last station and N.W. of 
— 72 
— 52 
the rock . 
+ 47 
-32 
— 1’20 
1 
Mean. • . . . 
+ 48 
-■40 
- 30 
From this it is evident that the station is affected by a regional lorce, the Hoii- 
zontal Components of wdiich are n — + 48, iv = — 40. Hence its line of action is 
N. 40' E., i.e., it appears to be affected by the large igneous masses to the north. 
