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POPULAR SCIENCE REVIEW. 
the stem, it turns on its centre. If two on one side are opened, it goes broad- 
side on. The channels are opened and closed by balanced valves, like engine 
throttle- valves. This little craft has been working successfully on the Clyde 
since November, and its constructors claim for the principle many advan- 
tages, especially for ships of war. 
Petroleum as a Substitute for Coal. — Some recent experiments with petro- 
leum oil used for heating water, gave results from which it was estimated 
that petroleum had more than three times the heating effect of an equal 
weight of coal. Mr. Richardson’s experiments at Woolwich, however, gave 
an evaporation of 12*96 to 13*66 lb. of water, by one pound of American 
petroleum ; 9*7 lb. of petroleum being burnt per square foot of grate per 
hour. With shale oil the evaporation was 10 to 10^ lb. of water per pound 
of fuel. The evaporative power of good coal may be taken, for comparison, 
at 8 to 8lr lb. per pound of fuel. Taking into account the saving of freight 
due to the better quality of the. fuel, and the saving of labour in stoking, it 
is possible that at some future time mineral oil may supersede coal in some 
of our ocean steamers. 
Frith of Forth Bridge. — Parliamentary sanction has been obtained for a 
bridge over the Frith of Forth, of a magnitude which gives it great scientific 
interest. It is to form part of a connecting-link between the North British 
and Edinburgh and Glasgow Railways. Its total length will be 11,755 feet, 
and it will be made up of the following spans, commencing from the south 
shore : — First, fourteen openings of 100 feet span, increasing in height from 
65 to 77 ft. above high-water mark ; then six openings of 150 ft. span, 
varying from 71 ft. to 79 ft. above high-water level ; and then six openings 
of 175 ft. span, of which the height above high-water level varies from 76 to 
83 ft. These are succeeded by fifteen openings of 200 ft. span, and height 
increasing from 80 ft. to 105 ft. Then come the four great openings of 500 ft. 
span, which are placed at a clear height of 125 ft. above high water spring 
tides. The height of the bridge then decreases, the large spans being 
followed by two openings of 200 ft., varying in height from 105 to 100 ft. 
above high water ; then four spans of 175 ft., decreasing from 102 to 96 ft. 
in height ; then four openings of 150 ft. span, varying in height from 95 to 
91 feet ; and lastly seven openings of 100 ft. span, 97 to 92 ft. in height. 
The piers occupy 1,005 ft. in aggregate width. The main girders are to be 
on the lattice principle, built on shore, floated to their position, and raised 
by hydraulic power. The total cost is estimated at £476,543. — Engineering , 
Jan. 5. 
MEDICAL SCIENCE. 
Who first discovered Trichina ? is a question which has given rise to con- 
siderable controversy during the past quarter. Dr. T. Spencer Cobbold has 
cleared up the whole question by a very interesting and able contribution to 
our contemporary The Lancet , in which he shows that the merit of the 
discovery is, as often happens, not due exclusively to one individual. 
“ Happily,” says Dr. Cobbold, “ the discovery of the actual flesh-worm itself 
