SCIENTIFIC SUMMAKY. 
327 
at the ends and least at the centre of the span. In the top boom or 
member of the braced arch the distribution of material is similar to that in 
the boom of an ordinary girder. But in the bottom or arched member the 
section is greatest at the ends and least at the centre of the span. Mr. 
Jenkin calculates that a braced arch of 500 feet span, of the same strength 
as the Britannia Bridge, would weigh only O' 65 ton per foot run, whereas 
the girders of the Britannia Bridge weighed 3 -8 tons per foot run. He 
states that there would be no difficulty in making the braced arch of cast 
iron in simple pipes, and that the cost of the superstructure of such 
a bridge would be only one-sixth that of a wrought-iron girder bridge. 
The braced arch is also suitable for construction in timber. 
Compound Engines. — In a paper on the Compound Engines fitted in 
H.M.S. Briton , by Mr. G. B. Bennie, it was stated that the ordinary con- 
sumption of fuel had proved not to exceed 2 lbs. per independent high 
pressure per hour. Supposing a ship to carry a given quantity of coal 
and to steam at a given rate, with a given expenditure of power, Mr. 
Bennie has calculated the following table of the relative length of time 
required to empty the coal bunkers, with ships fitted with engines of dif- 
ferent types : — 
Coal consumed Number of Days’ 
Type of Engine. per Ind. H. P. Steaming with. 
per Hour. 240 Tons of Coal. 
1. Improved Compound Engine . . . 2 . . 5 days 14 hours. 
2. Ordinary Engine with super- 
heaters and surface condensers . . 3^ . . 3 „ 4 „ 
3. Ordinary Injection Engine . . . . 4£ . . 2 „ 11 „ 
4. High Pressure Engine 6 . . 1 „ 21 „ 
Nothing could exhibit more clearly the importance of economical types of 
engine for steam navigation, and especially for heavily armoured ships of 
war. The actual consumption of fuel on the trial trips of the Briton varied 
from 1*515 to 1*981 lbs. per independent high pressure per hour. That on 
the trial trips of the Tenedos, with compound engines built by Messrs. John 
Elder & Sons, varied from 1*35 to 2*32 lbs. per independent high pressure 
per hour. 
MEDICAL. . 
Edinburgh University Philosophical Society . — The firsff session of the 
Edinburgh University Philosophical Society closed on Wednesday, April 5, 
Principal Sir Alexander Grant, Bart., delivering the valedictory address, 
the greater part of which consisted of an able criticism of the Darwinian 
theory of the descent of man. 
Influence of Non-nitrogenous Food on Man. — Dr. Parkes has been carry- 
ing on his inquiries into the subject of the influence of foods of different 
kinds on man. In the Proceedings of the Royal Society (March) he gives a 
long paper, in which we find it stated what is the influence of a non-nitro- 
genous diet on the system. For instance, the circulation was materially in- 
fluenced. Dr. Parkes says that with an equal pressure the lever was thrown 
