Sie if i, 4 veties Fa Aer. '5 9 > 
246 
Scelidosaurus, a form with some features pointing strongly 
towards the Ornithopoda. 
The Carnivorous inosauria now best known may all 
be placed at present in a single order, and this is widely 
separated from those that include the herbivorous forms. 
The two sub-orders defined include very aberrant forms, 
which show many points of resemblance to Mesozoic 
birds. Among the more fragmentary remains belonging 
in this order, but not included in the present classifica- 
tion, this resemblance appears to be carried much farther. 
The order Had/lopoda, which I have here referred to the 
Dinosauria, with doubt, differs from all the known 
members of that group in having the hind feet specially 
adapted for leaping, the metatarsals being half as long as 
the tibia, and the calcaneum ‘produced far backward. 
This difference in the tarsus, however, is not greater than 
may be found in a single order of Mammals, and is no 
more than might be expected in a sub-class of Reptiles. 
Among the families included in the present classifica- 
tion, I have retained three named by Huxley (Sce/ido- 
sauride, Iguanodontide, and Megalosauride), although 
their limits as here defined are somewhat different from 
those first given. The sub-order Compsognatha, also, 
was established by that author in the same memoir, 
which contains all the more important facts then known 
in regard to the Dinosauria. With the exception of the 
Hadrosauridz, named by Cope, the other families above 
described were established by the writer. 
The Amphisauride and the Zanclodontide, the most 
generalised families of the Dinosauria, are only known 
from the Trias. The genus Dystropheus, referred provi- 
sionally to the Sazrofoda, is likewise from deposits of 
that age. The typical genera, however, of all the orders 
and sub-orders are Jurassic forms, and on these especially 
the present classification is based. The Hadrosauride 
are the only family confined to the Cretaceous. Above 
this formation, there appears to be at present no satis- 
factory evidence of the existence of any Dinosauria. 
THE TAY AND THE FORTH BRIDGES 
a Male reconstruction of the Tay Bridge (if it really 
go on) by Mr. W. H. Barlow and the re-de- 
signing of the Forth Bridge by Mr. John Fowler 
and Mr. B. Baker will undoubtedly mark a new point 
of departure in the practice of British engineers. With 
the advent of railways there arose a generation of 
engineers who for some inexplicable reason ignored 
the traditions of their predecessors and gave no thought 
to wind pressure. Previous to this the question was 
always considered of vital importance by constructors. 
For example, Tredgold, writing some sixty years ago 
about roofs over building slips, directed special attention 
to the fact that such structures were “ much exposed to 
be racked and strained by high winds,’ and recom- 
mended certain proportions, based upon the assumption 
of the actual weight of the roof being 16 lbs. per square 
foot, and the pressure of the wind 40 lbs. per foot. He 
thus clearly warned engineers that in some instances the 
pressure of the wind and not the load governs the strength 
of the structure. Nevertheless so completely have British 
engineers ignored this condition that it may safely be 
said at least three-fourths of the railway bridges in 
Great Britain and Ireland have no lateral bracing or pro- | 
vision of any kind to enable them to resist wind pressure 
Even metallic arched bridges, which from their form must, 
in the absence of cross bracing, be necessarily in a state of 
more or less unstable equilibrium, form no exception to 
the rule. At Richmond, for instance, and at Kingston 
also, there are cast-iron arches about 100 feet in span, the 
lateral stability of which is dependent solely upon the 
8 inches or 10 inches wide flanges of the arched ribs. 
There is no lateral bracing nor are there any iron cross- 
* Quarterly Journal Geological Society of London, vol. vxvi. p. 34. 1870. 
a Be Mey EOE 
NATURE 
eae aE 
girders to bind the arched ribs together, and the lateral 
stiffness of a 10-inch flange over a span of 100 feet is 
more easily imagined than calculated. Within a few 
hundred yards of the Richmond Bridge is an anemometer 
which, according to the official returns, has not infre- 
quently recorded a pressure of 27 lbs. per square foot, but 
it is hardly necessary to say that no wind pressure even 
approximating to that amount could ever have taken 
effect on the bridge. 
Since the fall of the Tay Bridge the principles and 
practice of Telford’s day have been reverted to by British 
engineers, and the question of wind pressure has been 
most influential in determining the design and propor- 
tions of the new Tay and the proposed Forth Bridges. 
In the original Tay Bridge the type of pier foundation 
finally developed was, it may be remembered, a single 
cylinder of 31 feet diameter. This was satisfactory 
enough as regards vertical pressure, but in the new 
design it was lateral and not vertical pressure which 
governed the form of the pier’s foundation, and the latter 
will consist not of a single 31 feet cylinder but of two 23 
feet cylinders spread 32 feet apart centre to centre, and 
affording correspondingly increased lateral stability. Simi- 
larly, as regards the metallic piers resting on these foun- 
dations: originally these consisted of a group of cast 
iron columns, and as regards vertical pressure nothing 
could be better, for, as we have recently ascertained by 
tests, a hollow cast-iron column of ordinary proportions 
will carry more joad than either a wrought iron or a steel 
tube of equal weight. When the bending action of the 
wind upon a bridge pier is taken into consideration, how- 
ever, the steady vertical pressure due to the load becomes 
of comparatively little moment, and Mr. Barlow has very 
properly adopted wrought iron for the piers of the new 
Tay Bridge, and the Board of Trade have with no less 
propriety intimated, in their recent ‘‘ Memorandum of 
Requirements,” that piers made up of a group of small 
cast-iron columns will no longer be passed by the inspect- 
ing officers. 
The superstructure of the new Tay Bridge, no less than 
the piers, affords evidence of the provision which it is 
now thought necessary to make against the consequences 
of high wind pressures. Thus Mr. Barlow has provided 
three lines of defence against a train being hurled into 
the Tay, firstly, a guard balk of considerable height out- 
side each rail; secondly, a ballasted floor of sufficient 
strength to hold up a derailed locomotive at any point; 
and thirdly, a strong iron parapet. Most of these pro- 
visions will in all probability be insisted upon by the 
Board of Trade in future railway bridges. 
Turning now to the gigantic Forth Bridge, the influence 
of wind pressure in determining the design is beyond all 
precedent. The assumed lateral pressure of the wind 
upon the 1700 feet span girder is in fact no less than 50 
per cent. greater than the maximum rolling load, so that 
were it not for the influence of gravity on the mass of the 
bridge, the required strength would be greater laterally 
than vertically to the extent of one-half. The weight of 
steel in the 1700 feet girder is, however, so considerable, 
that the stresses both for rolling load and wind pressure 
are relatively less than in smaller bridges. ; 
The original design for the Forth Bridge by Sir Thomas 
Bouch was, it will be remembered, on the suspension prin- 
ciple. Except as regards the enormous drop in the sus- 
pension chains and the consequent unprecedented height 
of the piers, there was little to distinguish the proposed 
structure from an ordinary suspension bridge with stiffen- 
ing girder, and without the inclined stays characteristic of 
American suspension bridges. During the past forty 
years the suspension principle has been universally re- 
jected by engineers of all countries as unsuitable to the 
conditions of high-speed railway traffic, and the only 
reason for introducing it in the case of the Forth Bridge 
was the assumption that no other plan was commercially 
[ xan. 12, 1882 
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