346 _ * Analysts of Scientific Books. 
actually measured in them, but they are graduated one from another, 
and their errors are thus unavoidably perpetuated. Few of them 
have any adjustment for the change of level in the mercury of the 
cistern, and in still fewer is the adjustment perfect: no neutral point 
is marked upon them, nor is the diameter of the bore of the tube 
ascertained ; and in some the capacity of the cisterns is perpetually 
changing from the stretching of a leathern bag, or from its hygrome= 
tric properties. Nor would I quarrel with the manufacture of such 
play things; they are calculated to afford much amusement and in- 
struction ; but all I contend for is, that a person, who is disposed to 
devote his time, his fortune, and oftentimes his health, to the enlarge- 
ment of the bounds of science, should not be liable to the disappoint- 
ment of finding that he has wasted all, from the imperfection of those 
instruments, upon the goodness of which he conceived that he had 
good grounds to rely. The questions now of interest to the science of 
meteorology require the measurement of the five hundredth part of an 
inch in the mercurial column; and, notwithstanding the number of 
meteorological journals, which monthly and weekly contribute their 
expletive powers to the numerous magazines, journals, and gazettes, 
there are few places, indeed, of which it can be said that the mean 
height of the barometer for the year has been ascertained to the tenth 
part of an inch. ‘The answer of the manufacturer to these observa- 
tions is, that he cannot afford the time to perfect such instruments. 
Nor can he, at the price which is commonly given; for few people 
are aware of the requisite labour and anxiety. But who would 
grudge the extra remuneration for such pains? Not the man who is 
competent to avail himself of its application, Let the manufacture of 
playthings continue, but let there be also another class of instruments 
which may rival in accuracy those of the astronomer. It will, no 
doubt, be a part of the plan of the Committee of the Royal Society 
to establish a standard barometer, and to afford every facility of com- 
parison with it: so that any person, for scientific purposes, may have 
an opportunity of verifying an instrument; and it is to be hoped that 
they may proceed one step further, and take measures for ascertaining 
the agreement of the instruments at all the principal observatories, not 
only in this country, but in other parts of the world. 
‘‘ Nor is it in the construction of barometers only that the mete- 
orologist has to complain of that want of accuracy which is so essential 
to the progress of his science; the same carelessness attends the manu- 
facture of the thermometer, Few people are aware that they are all, 
even those which bear the first makers’ names, made by the Italian 
artists, who graduate them one from another, and never think of veri- 
fying the freezing and boiling points. The bulbs are all blown with 
the mouth, and very little attention is paid to the regularity of the 
tube. The register thermometers are particularly shamefully deti- 
cient. Those of Six’s construction are often filled with some saline 
solution instead of alcohol ; and in the best, the spirit is not exposed 
