THE BRITANNIA AND CONWAY TUBULAR IRON BRIDGES. 
335 
No of 
Station. 
Description of Station. 
Apparent 
Azimuth. 
Time of 
20 vibrations. 
Apparent 
Dip. 
1. 
External Carnarvonshire Station 
343 36 30 
s 
97-92 
+69 38 49 
+ 1 15 J5 
2. 
Carnarvon Abutment 
362 4 10 
60-43 
3. 
Middle of Carnarvon Land Tube 
(E.) 
366 41 40 
106-20 
+ 6 0 15 
4. 
Carnarvon Land Tower 
(E.) 
361 4 10 
115-60 
+ 8 14 15 
5. 
Middle of Carnarvon Water Tube 
(E.) 
361 58 20 
108-37 
- 2 55 38 
6. 
Britannia Tower 
(E.) 
355 50 50 
128-17 
- 5 23 38 
7 . 
Middle of Anglesey Water Tube 
(E.) 
351 0 0 
99-87 
- 3 12 23 
s. 
Anglesey Land Tower 
(E.) 
361 3 20 
111-57 
-15 19 0 
9. 
Middle of Anglesey Land Tube 
(E.) 
353 36 40 
112-23 
+ 16 16 0 
10. 
Anglesey Abutment 
(E.) 
352 50 0 
66-77 
+ 24 51 37 
11. 
12. 
External Anglesey Station 
163 16 30 
98-80 
+69 33 23 
+27 27 30 
Anglesey Abutment 
183 3 20 
68-93 
13. 
Middle of Anglesey Land Tube 
(W.) 
178 58 20 
124-30 
+ 16 39 15 
14. 
Anglesey Land Tower 
(W.) 
178 25 50 
1 1 7-90 
- 3 1 45 
15. 
Middle of Anglesey Water Tube 
(W.) 
183 54 10 
100-37 
+ 0 49 15 
IS. 
Britannia Tower 
(W.) 
181 50 50 
130-93 
+ 3 20 30 
17. 
Middle of Carnarvon Water Tube 
(W.) 
184 9 10 
106-63 
+ 1 19 45 
18. 
Carnarvon Land Tower 
(W.) 
178 12 30 
31410 
+ 9 17 45 
19. 
Middle of Carnarvon Land Tube 
(W.) 
171 5 50 
107-97 
+ 15 11 15 
20. 
Carnarvon Abutment 
(W.) 
171 13 20 
62-33 
— 4 4 0 
21. 
Holyhead Tower 
169 58 20 
12607 
+46 9 30 
22. 
Middle of Conway Bridge 
(S.) 
31 0 0 
173-10 
+32 17 0 
23. 
Chester Tower 
(S.) 
154 47 30 
131-30 
+35 11 7 
24. 
External Denbighshire Station 
263 34 30 
99-13 
+69 9 30 
+44 31 45 
25. 
Chester Tower 
323 10 0 
142-60 
26. 
Middle of Conway Bridge 
(N.) 
215 47 30 
171T7 
+ 18 30 45 
27. 
28. 
Holyhead Tower 
External Carnarvonshire Station 
(N.) 
338 40 0 
85 48 20 
105-93 
98-73 
+38 30 30 
+69 0 38 
It appears to me probable that the difference between the corresponding numbers at 
the two external stations of each bridge is purely accidental ; the only difference deserving 
attention is that at Conway, and there, as appears to me, the action of the iron bridge 
cannot explain it. I have therefore adopted for each bridge the mean of the two observed 
numbers for each element at the external stations as the true normal number peculiar 
to that locality ; and, as regards each pair of collateral stations in the two tubes of each 
bridge, I have thought it best to take the mean. Theoretically, it appears to me that 
the longitudinal action and the vertical action of each tube increase the longitudinal 
disturbance and the vertical disturbance in the other tube, but that the transversal 
horizontal action of one tube is scarcely sensible in the other tube ; this view, however, 
is not borne out by the final results. 
Taking the means, then, for the external stations as thus described, the numbers in the 
3rd, 4th, and 5th columns of the following Table are obtained. Assuming, in the case 
of each bridge, the total normal horizontal force =1, the normal horizontal force longi- 
tudinal to the bridge will = cosine azimuth of axis of bridge, the normal horizontal force 
transversal to the bridge, towards the right, =sine azimuth, and the normal vertical 
force = tangent of dip. Thus the 6th, 7th, and 8th columns are formed. 
Normal Local Elements. 
Nos. of Stations. 
Name of Bridge, 
Apparent Azimuth 
of axis of tube. 
Time of 
20 vibrations. 
Dip. 
Longitudinal 
force. 
Transversal 
force. 
Vertical 
force. 
1, 11. 
24, 28. 
Britannia 
Conway 
-16 33 30 
-95 IS 35 
s 
98-36 
9893 
69 35 41 
69 5 4 
+0-95850 
-0-09254 
+0-28500 
+0-99570 
+2-6882 
+26166 
