480 



Monday, March 16, 1857. 



Dr CHRISTISON, V.P., in the Chair. 



The folio-wing Communications were read : — 



1. Notice respecting Father Secchi's Statical Barometer, and 

 on the Origin of the Cathetometer. By Professor Forbes. 



A friend, who returned lately from Rome, has sent me some 

 copies of a pamphlet by Father Secchi of the CoUegio Romano, one 

 of which I lay on the table of the Society. 



It describes a barometer stated to be on a new construction. 

 The barometric tube is suspended from one arm of a balance, and 

 counterpoised. It is filled with mercury in the usual way ; but the 

 cistern into which it opens is fixed apart, and does not move with 

 the beam of the balance. It is evident, therefore, that the varying 

 pressure of the air on the exterior of the tube will require a chang- 

 ing counterpoise, and that the magnitude of the change may be 

 increased by enlarging the section of the tube, so that the alteration 

 of pressure may be indicated with any required delicacy. 



It is also obvious that, to use this barometer, the tube does not 

 require to be transparent, but may, for instance, be made of iron ; 

 only the internal section must be uniform throughout the range of 

 pressure. 



The idea of thus measuring barometric pressures appears so ol)vi- 

 ous that it is not likely to be really new. But I had also, when I 

 read the paper, a distinct recollection of having seen it described 

 many years ago. 



After a slight search I found it, accordingly, under the name of 

 the Steelyard Barometer (the tube being suspended from the shorter 

 arm of a steelyard, while the other points to the angular deviation 

 on a scale), in Rees, and others of the older Encyclopaedias (as in 

 the earlier editions of the Britannica^, in HuttorCs Mathematical 

 Dictionary, and in Gehler's Worterbuch. But, what is singular, 

 no inventor is assigned to the contrivance, except in the last-named 

 work, where it is desci'ibed generally as Morland's ; though Ilutton, 

 who is there cited as the authority, says nothing of it. 



