Nov. 30, 1882 | 
Columbz “ Bipositores,” as one of our systematists has 
proposed todo! After the pigeons Mr. Saunders places 
the sand-grouse as an intermediate order between the 
Columbez and Gallinz. This is certainly a better plan 
than that adopted by some of the more ardent reformers 
of the ornithic system—of uniting the sand-grouse in the 
same group with the pigeons, and thus spoiling the 
symmetry of the order Columbz. In this and in other 
particulars the new Editor of “ Yarrell’s Birds” show a 
judicious spirit, which cannot fail to make the results of 
his labours generally acceptable. 
Episodes in the Life of an Indian Chaplain. By a 
Retired Chaplain. (London: Sampson Low, Marston, 
Searle, and Rivington, 1882.) 
THISs interesting narrative of the adventures and vicissi- 
tudes of a devoted and single-minded Indian Chaplain, 
appears to be addressed to two classes of readers. A 
considerable portion must be considered more or less 
theological, and hence not applicable to the columns of 
NATURE; but running throughout the unambitious work 
is a considerable residue of facts and observations relating 
to zoology, which are never tiresome and sometimes 
original. In the days of his boyhood our author’s 
leisure time was given to his “different collections of 
natural history and antiquities,’ and after many years’ 
official duties he seems to have once more resumed his 
early tastes, on his appointment to the curatorship of the 
museum and secretaryship of the public gardens belonging 
to the Maharajah of Travancore. It is whilst employing 
his leisure in this vocation that the reader experiences 
more of the naturalist and less of the chaplain, but both 
phases are so kindly and modestly described, as to disarm 
criticism and at the same time promote an amiable 
impression of the writer. 
LETTERS TO THE EDITOR 
[Zhe Editor does not hold himself responsible for opinions expressed 
by his correspondents. Nether can he undertake to return, 
or to correspond with the writers of, rejected manuscripts. 
No notice is taken of anonymous communications, 
[The Editor urgently requests correspondents to keep their letters 
as short as possible. The pressure on his space is so great 
that it ts impossible otherwise to ensure the appearance even 
of communications containing interesting and novel facts.] 
Sir George Airy on the Forth Bridge 
Sir GrorGE Arry’s letter (v7de NATURE, vol. xxvi. p. 598) 
criticising Messrs. Fowler and Baker’s design for the Forth 
Bridge is so important, that I think it but right, as Iam not 
without experience on the subject, to make some remarks on the 
subject of it. Sir George Airy states :— 
1. ‘‘ That the proposed construction is, as applied to railway 
bridges, entirely novel.” This is not quite exact. There are a 
number of cantilever bridges in America; and I have, myself, 
used practically similar principles of construction and erection, 
on a largescale, with entire success, and find them so satisfactory 
that, for a very long span, I would not think of using any other, 
2. ‘‘The magnitude of its parts is enormous.” Undoubtedly 
they are—and all the more credit to the men who had the nerve 
to design them, 
3. ‘‘ There has been no succession of instances of the con- 
struction with rising degrees of magnitude which might furnish 
experimental knowledge of some of the risks of construction.” 
If this reason were sound, the same objection would have pre- 
vented the construction of the Conway, Britannia, and Saltash 
bridges, and Great Eastern steamer ; but so far from the state- 
ment being correct, the engineering profession has gained ample 
experience in the erection of the St. Louis, Kentucky River, 
Douro and Minnehaha bridges to give assurance that the Forth 
Bridge can be made a perfect success. 
4. ‘The safety of the bridge depends entirely on a system of 
end thrusts upon very long rods.” This is a very singular state- 
ment. What would become of the safety of the bridge in case 
there was no answering and complementary tension system 
equally exposed to danger from a ‘‘system of end pulls upon 
NATURE 
99 
very long rods” does not appear from Sir George’s letter ; nor 
does he seem to remember that the tests of the last few years 
show conclusively, that iron exposed to compression within its 
buckling limit is compacted in texture and strengthened by such 
use while, if subjected to continuous tension beyond two-thirds 
of its elastic limit, it is attenuated and weakened. 
5. ‘‘No reference is made t» theory applied to the buckling 
of rods under end thrusts.” None was necessary. Mr. Baker 
has designed struts, or columns—not rods, These members in 
the Forth Bridge are presumed to have stich a proportion of 
diameter to length that the question of buckling does not come 
into consideration. In America, columns of many shapes—in 
full-sized sectiois—have been tested in lengths of from 10 to 70 
diameters, and the value of these shapes, in pounds of resistance 
length 
diameter 
These results are now the common property of all English- 
speaking engineers. Sir George Airy’s remarks on long struts are 
the more extraordinary, as there isin England, in the upper chord 
of the Saltash Bridge, an example of a long strut without lateral 
support which is greater in its ratio of length to diameter than 
any member that I know of in the Forth design. Moreover, it 
is 455 feet long, near enouzh to the length of St. Paul’s Cathedral 
for him to contemplate in connection with that edifice, in pre- 
senting a picture to the people of London. 
6. ‘* The liability to ruinous disturbance by the lateral power 
of the wind acting with the leverage of the long brackets appears 
to be alarmingly vreat.”’ This liability to destruction by wind is 
common to all large spans ; but the danger is greater in the case 
of a suspension bridge than in any other (I speak with some 
knowledge on this point, having made the effects of tornadoes a 
special study for a number of years past, and having visited 
most of the bridge wrecks which have occurred in the States, 
from this cause, since 1858). So far as destruction by wind can 
be guarded against in the Forth design, it has afparently been 
done ; and the bridge will be vastly stronger in this regard than 
many other bridges in England which can be easily named, and 
about the stresgth of which there is supposed to be no question. 
To conclude:—The opinion of those American engineers 
with whom I have conversed on the subject, and whose expe- 
rience in building long-span bridges makes that opinion valuable, 
is uniformly to the effect that the design of Messrs. Fowler and 
Baker is well digested, perfectly practicable as to execution, 
and thoroughly permanent in character when finished. 
I may also add that three years since, when called on to de- 
sign a railway bridge for the crossing of the Great Colorado 
cafion, which was to be goo feet span and 750 feet above the river, 
linvestigated the relative merits and cost of the various systems— 
arch-suspension and cantilever with mid-span, Working draw- 
ings were made of each, and the result was, that the cantilever 
was adopted as being equally strong and stable—less liable to be 
affected by wind and thermal changes, aud decidedly more eco- 
nomical in first cost and easier of erection than either of the 
others. Iam, therefore, not surprised that the engineers of the 
Forth Bridge should have reached the same conclusion. 
CHARLES SHALER SMITH 
per square inch of section for each is definitely known. 
St. Louis, Mo., November rr 
The Aurora 
I HAD not the good fortune to see the very unusual phenomena 
which took place during the aurora of Noy. 17. It was, how- 
ever, well seen by four of the students of this College, Messrs. 
Sykes, Wildeblood, Thornhill and Wackrill. Although you are 
doubtless inundated with letters on the subject, I send a short 
account of the observation, as such an opportunity of determin- 
ing the height of an auroral light very rarely occurs. The 
commencement of the movement of the ‘* Whitehead-torpedo- 
shaped” streak of light does not appear to have been noticed by 
them; it passed however just below the moon, one observer 
thinks that its upper edge just grazed the lower edge of the 
moon. The light when close to the horizon bore due south- 
west, a position which has since been verified by bearings taken 
by a prismatic compass, The spot where the observers stood is, 
by the new ordnance map in lat. 51° 25’ 57” N., and long. 
oO 34/5” W. HERBERT MCLEOD 
Koyal Indian Engineering College, Cooper’s Hill, Nov. 24 
AT Ilford, Essex, on the 17th instant, at 6h. 4m. p.m. by a 
watch which was within 2m. of G, M. T., I witnessed, during 
