314 
On the Construction 
[Nov. 
meter are always liable to suspicion. But the evil is even greater than this, for the 
leakage may continue till the mouth of the tube within the cistern is exposed : air 
now enters and dislodges the mercury. The consequence is a lengthening of the co- 
lumn; but if this increase in the column should happen, as it often docs, to be coun- 
terbalanced by the fall occasioned by the sinking of the surface of the mercury in the 
cistern, a comparison made with a standard would fail to detect any derangement. 
The observer has his confidence restored, and is only finally undeceived (when the 
mischief is irremediable) by the intrusion of more hubbies ofair occasioning the column 
to lengthen, when from other considerations perhaps he knows it should be dimi- 
nishing. The instrument has now become useless, and the exorbitant sum originally 
paid for it lost, unless he will send it to England : for in none of these barometers that 
1 have seen is there a contrivance to allow of the purchaser supplying a new tube. 
The vexation in fact attending the use of oue < f these barometers is not to he told, 
it must be felt ; and to those who may think I have exaggerated the objections, I 
would recommend to make a journey through any difficult and wild country fur- 
nished with oue of them; and if they do not. obtain ample proof of the justice of my 
strictures, they will be more fortunate than 1 have been. 
The objections, however, which I have stated, do not apply to all portable barome- 
ters. Troughton’s for instance, are excellent, and in every respect indeed perfect 
save that of price, which is enormously high*. Berge’s are very good and cheaper ; 
but in a set of six that came to this country, and which I saw opened, not one ar- 
rived in order, the tubes were all broken, a proof they could not have been very por- 
table. The wooden cisterns which have their several screws fitted in England become 
deranged in this country from the great differences in the hygrometric state of the 
air ; add to which, though cheaper than Troughton’s, ttiey are still dear-f*. Dolloud 
makes very excellent instruments to order; their price, however, 1 have reason to 
think is also high*. ; as indeed must be, while made on the plan generally adopted : 
that which I am desirous of recommending, having but little work about it, must be 
cheap ; while I am of opinion, that in durability and portability, they exceed any 
yet made. 
Mr, Newman, an instrument maker in London, has lately brought out a barome- 
ter, in which he thinks he has successfully obviated the objections to Englefield’s 
plan, that of continual variation in the zero point, without any means of detecting it. 
He has substituted an iron cistern for the wooden one, by which leakage being 
entirely prevented, as he says, none of the derangements I have described, can pos- 
sibly arise, JBut as the iron cistern lias still a wooden lid, there is left a possibility of 
derangement, and that there is something more than a mere possibility, will be evident 
from the fact that I saw one of these instruments which was purchased for the late 
Dr. Abel, at a price of 200 Rs. and in which there was a considerable bubble of air. 
The instrument was in fact unserviceable. A second of these instruments I saw 
in the possession of another gentleman, who spoke favourably of it. But I after- 
wards understood from him, that being packed by the maker in a neat leathern 
case , with a strap attached for buckling round the body||, the. case leather which 
was made to fit too neatly , in the dry weather contracted, and in the efforts made to 
extract the instrument, it was broken. The maker having sent no spare tubes, an 
expensive instrument was thus rendered totally useless. This is an objection that 
does not apply to the form 1 am advocating. In this, the only expensive part is the 
brass-scale, which is always applicable to another tube. 
* 200 Rupees a piece. 
T About 300 Rupees the pair. 
X 350 Rs. the pair, I think. 
|( It is extraordinary that in making instruments for the Indian market, the artists 
of London will not advert to the difference in the habits of the two countries. Every 
thing appears to be made on the supposition that we are to carry the instruments 
ourselves, and is accordingly so contrived as to pack in the smallest compass — -The 
consequence is, that in the great and sometimes sudden atmospheric changes in this 
country, more inconvenience, annoyance, and even injury, is produced, than would he 
the consequence of their having twice or even ten times the bulk. In India there 
are no difficulties as to carriage ; — the great source of our troubles is small and curious 
packing obtained frequently by means ofintricate divisions, fastened only with £/«<?. 
Instrument makers should be told, that common glue will not resist a single rainy 
season in India, and thin or light wood work is of no sort of use. Everything intend- 
ed for this country should be massive and substantial, without any reference to 
portability. 
