102 
and contained about a dozen spines each. After a careful 
examination, I came to the conclusion that they were most 
likely to be the seat of the venomous propensities attributed to 
the insect, so I struck the back of my right hand against them 
two or three times to see what would be the effect. They were 
very brittle, and broke off as they entered the skin. I thought 
no more about it till about an hour had elapsed, when I 
experienced in the wrist adead pain which gradually extended 
to the arm-pit, followed by a swelling of the glands. 
For the whole day the pain was sufficient to render my arm 
useless ; hence I thought that there must be some poisonous 
secretion in the spines, for the irritation caused by fine points, 
even if barbed, would scarcely produce such an effect. The 
pain died away in the evening, unattended by any feverish 
symptoms whatever, for I was in excellent health at the time. 
Next day I examined several of the spines under the microscope ; 
they were not barbed, but hollow, and under pressure emitted a 
colourless transparent fluid, to which I attributed the poisonous 
qualities which caused me so much pain. A. M, FEsTING 
The Demagnetisation of Needles. 
Ir may not be generally known that magnetised needles, like 
those used in galvanometers and telegraphs, are easily and 
rapidly demagnetised in the neighbourhood of other magnets, 
when the fields of the two magnets are not coincident—that is, 
when their respective lines of force are not in the same 
direction. ; : 
A striking instance of this has just been brought to my notice. 
A tangent galyanometer used for taking daily readings of the 
escape of the current to earth upon wires, when they are dis- 
connected at their terminal points, was found constantly and 
gradually to be losing its delicacy. This was traced to be due 
to the demagnetisation of the needle. The needle was re- 
hardened and even changed but with the same effect. The gal- 
vanometer was fixed near some Wheatstone’s A B C instruments, 
which, being worked by magneto-electric currents, have power- 
ful permanent magnets within them. The galvanometer was 
shifted to the other side of the office, when the effect entirely 
ceased. 
Hence those who have delicate galvanometers should be care- 
ful to see that they are not kept in the field of permanent 
magnets, unless, as in the case of the mariner’s compass, they 
are free to move in the direction of the lines of forces of the 
magnetic field in which they lie, 
Southampton, May 20 W. H. PREECE 
Microscopes—Information Wanted - 
I am following up somé investigations and experiments in 
which I require certain data, which, however, aE cannot at present 
arrive at, not being in possession of sufficiently delicate and 
exact instrumental appliances. The information which I now 
desire to elicit from some more experienced observers than myself 
is of such importance as to be both useful and interesting to 
many of your readers, and I therefore crave your insertion of 
this communication, The information I require is all the more 
important as having a bearing upon many questions which are 
now attracting public attention, such as spontaneous generation, 
the initial stage and transitional forms of living organisms, also 
various researches in experimental physics, chemistry, &c. I 
desire to arrive at the following data :— 
1. What is the estimated dimensions of most minute particles 
of matter which can be visible, under any circumstances or con- 
ditions, under the highest powers of the microscope? I leave 
out of consideration (under this head) the question whether such 
matter is living or dead, organic or inorganic, or in fact regard- 
less of any of its properties whatever except its mere visibility as 
a minute portion of matter. Some observers speak of visible 
particles syaoth and gpy5yoth of an inch diameter ; this is 
surely near the limit. °F 
2. What is the best or most accurate method of arriving at 
an estimate of the dimensions of such minute objects as are too 
small to admit of actual measurement by any of the appliances 
now in use? Every microscopist knows from experience that 
objects may be distinctly visible, not as a mere point, but having 
an appreciable diameter, and yet be too minute for actual mea- 
surement to any degree of accuracy. ¢ 
3. Have the most recently constructed microscopic objectives, 
such as the 7yth or yth, any advantages over the 7th or y'yth 
[%une 5, 1873 
inch objectives in the determination of the data above referred 
to? and have immersion lenses any advantage in this respect? 
I find some difference of opinion on this point. Some micros 
scopists consider that a really first-class }yth with the use of deep 
eyepieces will enable us to see anything whatever which can be 
seen by any other objective of shorter focus, On the other 
hand, it is evident that a great number of the most experienced 
microscopists think otherwise ; and from the very fact of their 
purchase of such expensive high powefS, argue that such lenses 
are found to supply what other powers cannot accomplish. 
It appears to me that there is too much of vague and indefinite 
assertion in regard to the comparative powers and qualities of _ 
microscopic objectives, and it is very desirable that some more 
definite results should be arrived at. With what precision and 
accuracy the results of astronomical observations are made ! and 
taking into consideration that many of these results are obtained 
by different methods of observation, using different instruments, 
and by different observers, it is astonishing that the discrepancies 
and errors of observation are so small. It is generally admitted 
that the microscope is, to say the least, equally perfect, if not 
more so, than the telescope ; and we should therefore expect a 
corresponding degree of accuracy in the results of microscopical 
observations. There are no doubt many who, like myself, have 
hitherto worked with only the medium and low powers, but 
wish to be possessed of the improved objectives of high power, 
but from want of sufficient information it is difficult to make a 
suitable choice. H. H. 
Melbourne, Victoria, March 27 
Arctic Exploration 
THE story of the American Arctic Expedition under Mr. Hall 
is a wonderfully curious one ; but are we justified, from what 
we have been told, in coming to the conclusion that the part of 
the crew of the /o/avis, that has been rescued in so remarkable 
a manner, are “‘ deserters ?” 
As far as I have understood the reports which have appeared 
in the papers, none of the rescued men have said they were de- 
serters ; and until we hear what those who remained on board 
the Po/aris have to say, it appears to be unjust and reprehensible 
to bring so grave an accusation against men, possibly innocent. 
Should it so happen that Mr. Tyson and his companions are 
deserters, can we put faith in the correctness of any part of their 
story? 
There is certainly some mistake about the disposal of the six 
boats of the ship. As far as I can make out, only four, or at 
most five, are accounted for, namely, two abandoned in Smith 
Sound, and the two on the ice with Mr. Tyson, one of which 
was burnt for fuel, and the other, that in which they were when 
rescued, and which was taken on board the Zigris. io 
May 31 JOHN RAE 
The Westerly Progress of Cities 
In his work on the Atmosphere, M. Flammarion draws atten- 
tion to a peculiarity in the habits of our large towns which 
everyone mu:t have noticed. ‘*‘ The wealthy classes have a 
pronounced tendency to emigrate westward, leaving the eastern 
districts for the labouring populations, This remark applies 
not only to Paris, but to most great cities—London, Vienna, 
Berlin, St. Petersburg, Turin, Liege, Toulouse, Montpellier, 
Caen, and even Pompeii.” 
Having frequently remarked this ‘‘ westing” in many English 
towns, I have lately written to several friends, asking for definite 
information on th’s point, concerning the town in which they 
are resident. With scarcely an exception the reply of each 
showed, to alter Bishop Berkeley’s line a little, that :—‘* West- 
ward the course of fashion takes its way.” This is true, 
I believe, of Edinburgh, Dublin in former years at any rate, 
Glasgow, Liverpool, and Manchester, to some extent, Birming- 
ham, Leeds, Southamptom, and Bristol, No doubt many of 
your readers can very largely extend this list ; it would be inte- 
resting to collect wide information on this question, For sup- 
posing it established as a general fact, what an excellent specu- 
lation to buy up land in the west of a rapidly growing town like 
Leicester or Bradford? I am ignorant of these things; perhaps ~ 
it is common to do so already. 
Whence arises this tendency? It can hardly be an accident, 
nor can it be due to the direction of the river beside which the 
town may happen to be built, for in the towns named, many o 
