416 SECTIONAL TRANSACTIONS.—G. 
Wednesday, August 13. 
16, Mr. F. A. Datuyn.—The Engineer and Public Health. 
The writer attempts to divide the group of activities now relegated to 
Public Health organisations for administration into two classes, (1) those having 
to do with research and endeavour in the field of hygiene and nutrition, 
(2) those having to do with specific sanitation and the supervision of public 
water supplies, milk supplies, sewerage and sewage disposal, stream protection, 
garbage collection and disposal, and Municipal sanitation generally, including 
such projects as fly and mosquito control, rodent extermination, delousing 
stations, &c., and suggests that much of the work of the latter division is of 
an engineering nature, and could with advantage be left to the direction of 
engineers and biologists, releasing the medical personnel for their distinctive 
field, and possibly freeing the public mind of the notion that Public Health is 
necessarily a medical science. 
17; Mr. J. D. Watson.—The Part Bio-aeration may yet Play in 
Disposal of Sewage. 
18. Mr. E. A. Warson.—Cobalt Magnet Steels. 
The paper, intended as a general review of the position at the present 
time, is divided into three sections : 
1. Historical, traces the development of the steels, and describes the present 
position of the industry, and gives notes as to its future prospects. 
2. Describes the various steels available, giving data of their composition 
and magnetic properties. It traces the effect of cobalt on magnetic properties 
of a given series of steels, and gives data as to heat treatment. 
3. Gives a brief account of the economic factors governing the application 
of cobalt magnet steels, with data showing the conditions under which the use 
of a cobalt steel is economically justifiable 
19: Mr. R. 8. WurppLte.—Some new Recording Instruments. 
20. Mr. A. E. Wynn.—An Economical Design for Arch Centres. 
The centring design for a two-ribbed concrete arch bridge of 200 ft. span 
and 40 ft. total rise from river bed to crown, built at Pulaski, N.Y., in 1922, 
shows some interesting features, in that short lengths and small sizes of timber 
were used, necessitated by the local available supply, in the use of spikes instead 
of bolts and because of the high stresses allowed in the timbers. 
Three-post bents set on concrete piers in the river supported each rib, the 
posts being 6 in. by 6 in., in three lengths of 12 ft.; between the posts were 
6 in. by 6 in. caps longitudinally and transverse. The top caps were 6 in. or 
8 in. by 12 in., supporting 3 in. by 12 in. stringers, 12 in. apart, cut to curvature, 
and Z in. by 6 in. t and g lagging. 
All timbers were long leaf yellow pine. The bents were so spaced longi- 
tudinally that all members were stressed up to the maximum allowable of 
2,000 lb. per sq. in. in bending and 800 lb. per sq. in. in bearing. 
No hardwood wedges were used between posts and caps except for one set 
used in adjusting and lowering the centring. 
The posts carried 10 to 13 tons apiece, but the bite in the caps did not 
amgrat to as in. each, the total deflection of the crown during pouring being 
only 4 in. 
gd WR a ea i cheat ts rs she rate Ade etinaihinnbiin ox -* 
——_ 
All bracing was 2 in. by 6 in., spiked into the posts with 20d spikes, no ~ 
bolts being used anywhere. This was considered more effective in adding to — 
the stiffness and was a saving in cost and time. The centring was erected in 
fifteen days and stripped in four days. The stripping was done by first passing 
ropes around the stringers and lagging, tying them up to the ribs, then pulling 
over the bents bodily on to the ice and finally dropping the suspended stringers - 
and lagging. The timber breakage was negligible and the cost was exceedingly 
