ON MAGNETICAL AND METEOROLOGICAL OBSERVATIONS. 153 



the necessity of an immense mass of laborious and exhausting penmanship 

 and computation. Self-registering instruments henceforward will prove 

 yearly more and more the main dependence of meteorological inquiry, and 

 indeed of inquiry in every department of science in the saiue phase of its 

 progress : and their improvement, simplification and adaptation to the pur- 

 poses of affording mean results on the one hand, and on the other the tracing 

 out of curvilinear projections (the true "collective instances" of the Baco- 

 nian philosophy) in a state ready for immediate use, ought to be regarded as 

 one of the most important, perhaps the most important point to which mecha- 

 nical ingenuity, guided by scientific knowledge, can be directed. The great 

 object which ought to be kept steadily in view, is so to dispose the apparatus 

 that corrected results shall be registered, if possible, and if not, that the cor- 

 rections to be applied shall be registered at the same instant, and on the same 

 scale with the observed elements, so that they can be readily applied to the 

 projected curves by mere mechanical or geometrical superposition. 



In this point of view a barometer which shall register its readings corrected 

 for temperature would be of the utmost value. This does not appear be- 

 yond the reach of a moderate expenditure of thought*, and your Committee 

 would earnestly recommend it to the consideration of artists. 



Meanwhile it is with satisfaction that we refer to two constructions of self- 

 registering barometers which have recently come to our knowledge : — one 

 by Mr. Bryson, recently published in vol. xv. of the Transactions of the 

 Royal Society of Edinburgh (to which apparatus he has since added a self- 

 registering thermometer for the corrections, and a self-calculating disc at- 

 tached to the reader, which exhibits the monthly means without calculation) : 

 the other instrument of the kind in question is the invention of M. Kreil, 

 director of the observatory at Prague, who terms it a baro-thermometragraph, 

 and who has also constructed a similar instrument (the thermo-hygrometra- 

 graph) for registering hygrometric indications. An instrument of this kind 

 is now on its way to this country, having been constructed under the imme- 

 diate superintendence of its inventor. 



Finally, your Committee beg to recall to the recollection of the Association, 

 that the duration of the magnetic and meteorological observations now in 

 progress will cease with the year 1845, and that therefore it will be highly 

 necessary that before that time — and in fact, if possible, at or before the 

 next meeting of the Association, — the important question should be seriously 

 taken into consideration, whether any endeavour ought or ought not to be made 

 to obtain from the several governments which have supported the existing ob- 

 servatories further support — a very grave question, which has been already 

 distinctly brought under the notice of your Committee by one of their most 

 active coadjutors, M. Kupffer, director of the Russian magnetic observatories, 

 and which it is highly proper should be considered in every point of view 



* An approximate compensation by the counteracting pyrometric expansion of an inva- 

 riable length of mercury or lead is easily accomplished, but this would be subject to occasional 

 error, amounting to nearly one-fifteenth of the total amount of the temperatm'e correction. 

 The pyrometric compensating column must be variable in its length in the ratio of the un- 

 corrected length of the mercurial column, measuring the pressmre. If however the instru- 

 ment be mounted in a situation of which the variations of temperature are very slight, as in 

 a cellar, or at the bottom of a mine, shaft, or even a well (which, as there is no occasion to 

 approach it, except for the purpose of renewing the cyUnders, would be liable to httle objec- 

 tion), the error thus entailed would be so reduced in effect, as to disappear, for any but the 

 very nicest purposes. Indeed the barometric part of the apparatus might be buried in the 

 earth (allowing only enough access of air to propagate the pressure), the registering apparatus 

 only being above ground. 



