488 
large scale surveys of portions of British districts in the Madras 
and Bombay Presidencies, which, though undertaken originally 
for purely fiscal purposes by revenue and settlement officers 
working independently of the professional survey, have latterly 
been required to contribute their quota to the general topography 
of the country. And of late years a survey branch has been 
added to the Forest Department, to provide it with working 
maps constructed for its own requirements on a larger scale than 
the standard topographical scale, but on a trigonometrical basis, 
and in co-operation with the Survey Department. But this brief 
capitulation gives no sort of idea of the vast amount of valuable 
topographical and other work for the requirements of the local 
Administrations and the public at large—always toilsome, often 
perilous—which has been accomplished, quite apart from and in 
quantity far exceeding the non-graphical and more purely scientific 
work which I have been describing. Its magnitude and variety are 
such that a mere list of the officers who have taken prominent 
shares in it, from first to last, would be too long to read to you. 
Three names, however, I must mention: frst, that of General 
Sir Henry Thuillier, who became Suryeyor-General on the same 
day that I succeeded to the superintendence of the Great Trigo- 
nometrical Survey, and with whom I had the honour of co- 
operating for many years; under his administration a much 
larger amount of topography was executed than under any of 
his predecessors, and a great impetus was given to the litho- 
graphic, photographic, engraving and other offices in which the 
maps of the survey are published ; secondly, that of Colonel 
Sconce, who became Deputy Surveyor-General soon after my 
accession in 1878 to the Survey-Generalship, and with whom I 
was associated for some years, much to my gratification and ad- 
vantage, in various matters, but more particularly in the esta- 
blishment of cadastral surveys on a professional basis at a 
moderate cost, to render them more generally feasible, which 
was a matter of the utmost importance for the administration of 
the more highly populated portions of the British provinces ; 
and ¢hirdly, that of Lieutenant-Colonel Waterhouse, who has 
for many years superintended the offices in which photography 
is employed, in combination with zincography and lithography, 
for the speedy reproduction ex masse of the maps of the Survey, 
and has done much to develop the art of photograyure, whereby 
drawings in brushwork and mezzotint may be reproduced with a 
degree of excellence rivalling the best copperplate engraving, 
and almost as speedily and cheaply as drawings in pen and ink 
work are reproduced by photo-zincography. 
Mr. Clements Markham’s Memoir on the Indian Surveys gives 
the best account yet published of the several graphical surveys 
up to the year 1878. In that year the Trigonometrical, Topo- 
graphical, and the Revenue branches, which up to that time had 
constituted three separate and almost independent departments, 
were amalgamated together into what is now officially designated 
““the Survey of India.” In the same year the chronicle so well 
commenced by Mr. Markham came to an end on his retirement 
from the India office—unfortunately, for it is a work of excel- 
lence in object and in execution, and most encouraging to Indian 
surveyors, who find their labours recorded in it with intelligent 
appreciation and kindly recognition. 
During the present meeting, several papers by officers of the 
Survey will be read—one by Colonel Barron, in person, on the 
cadastral surveys in the organisation of which he has taken a 
leading share ; by Major:Baird, on the work of spirit-levelling, 
which he superintends conjointly with the tidal observations ; by 
Colonel Godwin Austen, on Lieutenant-Colonel Woodthorpe’s 
recent journey from Upper Assam to the Irawadi river; by 
Colonel Branfill, on the physical geography of Southern India ; 
and by Colonel Tanner, on portions of the Himalayas, and on 
recent explorations in Southern Tibet. Major Bailey will also 
read a paper on:the forest surveys. 
SECTION G 
MECHANICAL SCIENCE 
OPENING ApDpREss BY B. BAKER, M.INsT.C.E., PRESIDENT 
OF THE SECTION 
Two hundred and fifty-seven Presidential Addresses of one 
kind and another have been delivered at meetings of the British 
Association since the members last mustered at Aberdeen. I 
need hardly say that the candid friend who informed me of this 
interesting fact most effectually dispelled any illusion I may 
NA TOL 
= r 
[Sept. 17, 1885 
have previously entertained as to the possibility of preparing an 
address of sufficient novelty and suggestiveness to be worthy of 
your attention, and I can only hope that any shortcomings will 
be dealt with leniently by you. One compensating advantage 
obviously belongs to my late appearance in the field—I have 
257 models of style upon which to frame my address. My dis- 
tinguished predecessor, Sir Frederick Bramwell, has a style of 
his own, in which wit and wisdom are combined in palatable 
proportions ; but were I to attempt this style I should doubtless 
incur the rebuke which a dramatic critic of Charles the Second’s 
time administered to a too ambitious imitator of a popular 
favourite: ‘‘ He’s got his fiddle, but not his hands to play on’t.” 
I must search further back than last year, therefore, for a model 
of style, and the search reminds me that I labour under a double 
disadvantage : firstly, that only two addresses intervene between 
the present one and that of my partner, Mr. John Fowler, with 
whom I have so long had the honour of being associated, and 
whose professional experiences, as set forth in his address, are 
necessarily so largely identical with my own; and, secondly, 
that within the same period I have read before this Section two 
somewhat lengthy papers on the work which is at present chiefly 
engaging the attention of Mr. Fowler and myself—the great 
Forth Bridge. 
Although, for the reasons aforesaid, I am conscious that my 
address may fail in novelty, I cannot honestly profess to feel a 
difficulty in preparing an address of some kind, for the subjects 
embraced under the head of ‘‘ Mechanical Science” are so in- 
exhaustible that even the youngest student might safely accept 
the responsibility of speaking for an hour on some of them. 
Prof. Rankine, addressing you thirty years ago, said it was well 
understood that questions of pure or abstract mechanics form no 
part of the subjects dealt with in this Section. With character- 
istic clearness of conception and precision of language he told 
you what the term ‘‘mechanical science” meant, and, after 
thirty years’ interval, his words may be recalled with advantage 
to every one proposing to prepare an address or report for this 
Section. ‘‘ Mechanical science,” said Prof. Rankine, ‘‘ enables 
its possessor to plan a structure or machine for a given purpose 
without the necessity of copying some existent example; to 
compuie the theoretical limit of the strength and stability of a 
structure or the efficiency of a machine of a particular kind ; to 
ascertain how far an actual structure or machine fails to attain 
that limit, and to discover the cause and the remedy of such 
shortcoming ; to determine to what extent, in laying down 
principles for practical use, it is advantageous for the sake of 
simplicity to deviate from the exactness required by pure science ; 
and to judge how far an existing practical rule is founded on 
reason, how far on custom, and how far on error.” There is 
thus an ample text for many discourses ; but, as I am not writ- 
ing a treatise on engineering, but merely delivering a. brief 
address, I will confine my attention at present to a particular 
case of the branch of mechanical science referred to in the last 
clause of Prof. Rankine’s definition, and will ask you to con- 
sider how far the existing practical rules respecting the strength 
of metallic bridges are ‘‘ founded on reason, how far on custom, 
and how far on error.” 
The first question obviously is, What are the rules adopted by 
engineers and Government departments at the present time ?—and 
it is one not easily answered. I have for some time past been re- 
ceiving communications from leading Continental and American 
engineers, asking me what is my practice as regards the admiss- 
ible intensity of stress on iron and steel bridges, and in replying I 
have invited similar communications from themselves. As a 
result I am able to say that at the present time absolute chaos 
prevails. The old foundations are shaken, and engineers have 
not come to any agreement respecting the rebuilding of the 
structure. The variance in the strength of existing bridges is 
such as to be apparent to the educated eye without any calcula- 
tion. If the wheels of a miniature brougham were fitted to a 
heavy cart the incident would excite the derision even of our 
street boys, and yet equal want of reason and method is to be 
found in hundreds of bridges in all countries. It is an open 
secret that nearly all the large railway companies are strengthen- 
ing their bridges, and necessarily so, for I could cite cases where 
the working stress on the iron has exceeded by 250 per cent. 
that considered admissible by Jeading American and German 
bridge-builders in similar structures. ; ‘ 
In the case of old bridges the variance in strength is often 
partly due to errors in hypothesis and miscalculation of stresses. 
In the present day engineers of all countries are in accord as to 
