124 REPORT—1852. 
large scale with tubular and lattice beams, in connection with some large bridges 
which he has lately erected on the Belfast Junction Railway, and especially for the 
design for the Boyne Viaduct, the calculations for which, and the working out of the 
details, were entrusted to him by Sir J. Macneill and the directors of the company : 
the results show the high importance of an accurate consideration of the various strains 
to which each bar is subjected, and the separate and different effects of a passing and 
constant load. ‘he paper proceeded to explain how these calculations were to be 
carried out, by resolving each part of the load into its separate effect of tension and 
compression on every bar in the same system, and on the top and bottom, and adding 
to these results the constant effect of the weight of the structure, and the results or 
maxima strains for every bar were shown in diagrams, as also a geometrical elevation 
of the strains ; the general result is, that in ordinary trussed or lattice-bridges the bars 
sloping downwards towards the bottom at the centre were subject toa tensile, and 
the others to a compressive strain, and that these strains increase nearly in an avith- 
metical proportion towards the points of support; but that they pass each other for 
some distance at the centre, so that a certain number of bars are subject to a small 
amount of both tensile and compressive strain. The geometric elevation showed the 
very small proportion the strains in the sides bear to those in the top and bottom, 
and therefore the inutility of making the sides solid plates, whilst from the amount 
of compression a single plate does not give rigidity. The paper went on to compare 
the relative value of single systems bracing with the lattice, and to consider the true 
angle of ceconomic bracing which appeared to be 45°; also how far the calculations are 
affected by riveting together the bars at their intersections. The paper further pro- 
ceeded to the practical application, and to the details of construction, explaining 
some improvements introduced by the author, both as to the mode of construction of 
the compression bars, which by him are made to form lattice beams, as also in the 
connection of plates by means of which he proposes to rivet plates with a very slight 
loss of their sectional area. An isometrical projection of a lattice beam was also ex- 
hibited carrying out the principles laid down. 
A series of Observations on the Discharge of Water from actual Experiment. 
By J. F. Bateman, CLE. 
Mr. Bateman stated that his experiments proved the accuracy of formule esta- 
plished Dy Chevalier Dubuet, for calculating the mean velocity of water in the separate 
channels, 

On the Evolution of Gas in Wallsend Colliery. By GrEorGE CLARKE. 
Communicated by Professor PHILLIPS. 
This paper relates to one of the coal-mines in the district of the Tyne which 
have been rendered remarkable for the frequent explosion of the inflammable 
gas which they yield, and the loss of life which has in so many cases been the conse- 
quence. The colliery in question has been wrought for many years in safety, by the 
exclusive use of the Davy lamp, though it evolves every moment abundance of gas. 
A district of this colliery, covering about fifty acres, was effectually walled up, in con- 
sequence of the immense discharge of gas that was continually taking place. A pipe 
was led from this enclosed portion up through the mine and for forty feet above the 
surface, and from this pipe there has been a constant discharge of gas for the last 
eighteen years. This gas has been inflamed, and in the roughest and most stormy 
weather it has burned without intermission; and were it as rich in naphtha as ordi- 
nary carburetted hydrogen, it would illuminate the country for miles round. -Two 
water-pressure gauges were fixed, one to the pipe at the surface of the earth, and the 
other at the bottom of the mine; and the results were that, whilst the pressure in the 
mine was only 4%;ths of an inch on an average, that at the top of the pit was upwards 
of four inches. 'rom observation in these mines, it appears that discharges of fire-damp, 
governed by atmospheric pressure, have taken place before depressions of the baro- 
meter, and that as an indicator of danger that instrument cannot be implicitly relied 
on. A fact somewhat similar was first observed by Professor Daniell, in his researches 
at the Royal Society, where the water barometer indicated the change of pressure an 
hour earlier than the usual mercurial standard barometers constantly employed for 
observations. 

