THERMOMETER AND PYROMETER. 



Santorio expressly claims the inven- 

 tion as his own,* and he is supported 

 by Borelli t and Malpighi ; $ the title 

 ofDrebbel is considered as undoubted 

 by Boerhaave and Musschenbroek.|| 

 It would now be difficult, perhaps, to 

 decide the controversy ; but it is worthy 

 of remark, that Santorio, who was born 

 in 1561, and died in 1636,5[ did not 

 publish his claim to the invention till 

 1626;** and, although thermometers 

 are alluded to by Robert Find, within 

 the first quarter of that century, yet 

 as he travelled both in Germany and 

 Italy for six years, we can draw no 

 inference from that circumstance. Cer- 

 tain it is, that thermometers were con- 

 structed about the same time, both in 

 Italy, and in Holland, on the same prin- 

 ciple ; and though the instruments of 

 Drebbel were well known in Holland 

 and England, before the fame of San- 

 torio appears to have reached the 

 North-West of Europe, the most re- 

 cent writers have generally considered 

 the latter as the real inventor of the 

 thermometer. It is, however, by no 

 means improbable that each may be 

 justly entitled to the merit of a dis- 

 coverer. 



Be this as it may, the instrument 

 was, from its imperfect construction, 

 of little use in the hands of either, and 

 required the successive labours of dif- 

 ferent philosophers to render it a tole- 

 rably accurate indicator of the varia- 

 tions of temperature. 



The thermometer ascribed to San- 

 torio and to Drebbel, is pre- p> , 

 cisely the same in form and ' 

 principle. It consists of a glass 

 tube, with a ball blown on one 

 of its extremities A, (fig. 1,) 

 and having the other end 

 open. A portion of the air in 

 the ball is expelled by heat, 

 and then the open end of the 

 tube is immersed in any liquid 

 contained in the cup c. As the 

 ball cools, the included air 

 diminishes in volume, and the 

 liquid is forced into the stem, 

 as at b, by the pressure of cl 

 the atmosphere, until it re- 

 places the volume of air which was 



* Comment, in Galen, et in Avicen. 

 t De Motu Animalium. Prop, clxxv. 

 J Opuscula Posth. p. 30. 

 Klementa Chemise, torn. i. p. 152. 

 IIElem. Phil. Nat. 780. Tentam Exp. Acad. 

 Cim. 



II Tiraboschi Storia, torn. viii. P. 1,323. 

 ** Commentaria in Avicennam. 



expelled by the heat. When a 

 heated body is applied to the ball A, 

 the air will again be expanded, and 

 depress the liquid in the stem ; and, if 

 this stem be a cylinder, a scale of equal 

 parts applied to it will enable the ob- 

 server to form some idea of the dif- 

 ference between the relative tempera- 

 ture of bodies applied to the ball. On 

 the removal of the heated body, the 

 volume of the included air again di- 

 minishes, and the liquid again rises in 

 the stem by atmospheric pressure, un- 

 til the elasticity of the air within the 

 instrument is in equilibria with that of 

 the surrounding atmosphere. Instru- 

 ments constructed on this principle are 

 termed air thermometers ; because their 

 action depends on the elasticity of air ; 

 and from their having been originally 

 employed to mark the changes of atmo- 

 spheric temperature, they are described 

 by the older writers under the name of 

 weather-glasses; a denomination also 

 given to barometers. 



Drebbel appears to have devised a 

 variety of the instrument more delicate 

 in its indications. The globular form 

 of the common bulb, and its small size, 

 rendered it less susceptible of slight 

 changes than a flattened bulb of larger 

 diameter ; and Boerhaave describes the 

 bulb of Drebbel's thermometer, as com- 

 posed of two shallow segments of large 

 spheres, as in'jtfg-. 2. A, united at their 

 edges, and in/g-. 2. B, where it is seen 

 in profile. 



Fig. 2. A. Fig. 2. B. 



In the obscure, and often almost un- 

 intelligible, writings of our countryman, 

 Dr. Robert Flud, published about the 

 beginning of the seventeenth century, 

 frequent mention is made of the ther- 

 mometer, or, as he calls it, speculum 



