168 History of Mechanical Inventions. 



This instrument would be greatly improved if a thermometer which re- 

 gistered the lowest descent of the mercury, and having its bulb covered 

 with wetted paper, were placed in each of the openings. By examining 

 the state of the thermometer after a given time, we would be enabled to 

 determine what had been the state of the winds during that time. In this 

 way we would obtain, in the absence of the observer, a record of veering 

 or changing winds, and would gather much information respecting what 

 took place during a certain period. It would be easy to keep the bulbs of 

 all the thermometers constantly wet. A greater number too might be used, 

 and they might be so placed that one of them would not be affected by a 

 wind blowing at any given inclination to the direction of the face on which 

 it is placed. — En. 



8. Xotice of a Pyrometer for measuring high Temperatures. By James 

 Prinsep, Esq. Benares. 

 After trying various plans for pyrometers, Mr Prinsep gave the prefer- 

 ence to one founded on the following principles : — 



1. That the fusing points of the pure metals are fixed and determinate. 



2. That those of silver, gold, and platinum, comprehend a very exten- 

 sive range of temperature ; and 



3. That between these three fixed points in the scale as many interme- 

 diate ones as may be required will be obtained, by alloying the three me- 

 tals together in different proportions. When such a series of alloys has 

 been once prepared, the heat of any furnace may be expressed by the alloy 

 of least fusibility which it is capable of melting. The determinations af- 

 forded by a pyrometer of this kind will, independently of their precision, 

 have the advantage of being identifiable at all times and in all countries. 

 The smallness of the apparatus is an additional recommendation, nothing 

 more being necessary than a little cupel, containing in separate cells the re- 

 quisite number of pyrometric alloys, each of the size of a pin's head. The 

 specimens melted in one experiment need only to be flattened under the 

 hammer, in order to be again ready for use. For the purpose of concisely 

 registering the results, the author employs a simple decimal method of 

 notation, which at once expresses the nature of the alloy, and its corre- 

 spondence with the scale of temperature. As the distance between the points 

 of fusion of silver and gold is not considerable, the author divides the dis- 

 tance on the scale into ten degrees ; obtaining measures of each by a suc- 

 cessive addition of ten per cent, of gold to the silver, the fusion of which, 

 when pure, marks the point of zero, while that of gold is reckoned at ten 

 degrees. From the point of fusion of pure platina to that of pure gold, 

 the author assumes 100 degrees, adding to the alloy which is to measure 

 each in succession one per cent, of platina. The author then enters into 

 a detailed account of the method he employed for insuring accuracy in the 

 formation of the requisite series of alloys, and cf various experiments un- 

 dertaken to ascertain their fitness as measures of high temperatures. The 

 remainder of the paper contains the recital of the author's attempts to de- 

 termine, by means of an apparatus connected with an air thermometer, the 



