VOL. XL.] PHILOSOPHICAL TRANSACTIONS. iQQ 



diagonal barometers ; for after some time, by the various rising and falling, and 

 changes of the weather, of heat and cold, the small particles of air interspersed 

 in the mercury, have got together in a larger mass, as they will incline by at- 

 traction, which will separate the mercury ; and that quantity of air will be dilated 

 by heat, and contracted by cold, so as to spoil the design of the instrument. 



Besides, there is such a cohesion or attraction of the mercury to the tube, 

 especially in the small ones, that after some time, the mercury that is not truly 

 cleansed from its dross, and purged of all its air, in remarkable changes of the 

 weather, will neither rise nor fall. All which embarrasment is taken off, and 

 the difficulties surmounted, in 



Mr. Cha. Ormes Improvements of the Barometer, by the Method following : 



First, The quicksilver is all purified from its dross and earthy particles by 

 distillation ; and when the tube is filled by a pound and half, or 2, or 3 lb. of 

 mercury, and all the air got out by the methods used in filling tubes, then the 

 remaining air is got out by such an intense heat of fire as makes the mercury 

 boil; by which ebullition an innumerable quantity of small particles are emitted, 

 and blow with a great velocity at the open end of the tube, till all the air is 

 quite cleared out ; which operation is continued for the space of 4 hours : and 

 when no more bubbles would rise in the tube, it remained whole, with its mer-. 

 cury of a most lively sparkling brightness, with this difference only, that the 

 mercury, so purged of its air, did not fill the tube so high as when first put in, 

 by about 1 inches ; which is a plain demonstration, that in that tube, which 

 was 49 inches long, there was interspersed in the mercury at first filling it, so 

 much air as would fill 2 inches of the said tube, which was a 24 th part of the 

 said space. In this way every part of the mercury boiled for a long time, and 

 the tube became gradually so red-hot, that with a warm knife impressions couI4 

 be made in any part of it. 



And this I the rather mention, by reason I have heard several persons, and 

 those not incurious, affirm it was impossible. 



The Perfection of these Barometers, by which they exceed all others ever ob- 

 served, in the following Particulars. — -1. They are sensible of the most minutq 

 changes of the air. 



2. They fcretel the weather by a much longer space of time than others, as 

 mostly 20 hours, sometimes 36 or 48 hours : nay, before great tempests, and 

 such rains as cause great floods, for a much longer time before they happen. 



3. Though they are so sensible of such minute changes of the air, yet the 

 most intense heat will not raise them a hair's-breadth, nor the greatest cold 

 make them fall. This shows that they are perfect barometers, and not in any 

 degree thermometers. 



