146 Decisions on Disputed Inventions. 



expansion of the air in the ball which pushes down the fluid, is marked 

 upon a scale attached to the tube. In the second thermoscope, the air- 

 ball is at the lower end of a tube like the letter /, and there is a small 

 hole in the ball at the upper end, to allow the coloured fluid to risa 

 when the air in the lower ball is expanded by heat. 



The third thermoscope, which is the differential thermometer, is a 

 combination of these two, and is represented in Plate II. Fig. 20. The 

 following is Sturmius's own description of it. " Tertium e duobus 

 prioribus ferme compositum sic habebat : Parato posteriori genere 

 ABCD plane ut antea, super imposita est et firmiter agglutinata ejus 

 extremitati apertae D, sphaerula E in eum finem seorsim fabrefacta; 

 ita ut jam aeri nee ingressus nee egressus pateret. Hie, dum calida 

 manus applicabatur sphaerulae E, summa superficies spiritus inclusi C 

 descendebat ; si frigidum quippiam, ascendebat : contrarium autem plane 

 fiebat admotis istis sive calidis sive frigidis ad inferiorem sphaerulam 

 A. Solius viro aeris liberi calori exposito instrumento, sphaera A (quam 

 notetur angustiorem fuisse notabiliter altera E) semper prevalebat et 

 sola operabitur : ita scil. ut incalescente magis aere liquorem a C suble- 

 varit, ac ad ascensum cogeret ; ad descensum contra, cum calor aeris 

 remitteret et plus frigoris succederet. Notandum tamen ascensus istos 

 ac descensus liquoris, sive a liberi aeris, sive ab admotarum rerum ca- 

 lore vel frigore causatos, ad minus notabile spatium se extendisse, seu 

 vias breviores confecisse, quam in genere precedenti." Page 49, SO. 



In explaining the theory of the instrument, he goes on, 



" In tertio genere nihil equidem agit aer extemus, utpote penitus 

 exclusus ; eodem tamen res recidit, cum et superus aer EC et inferus 

 AB ad equalitatem virium redacti, medium aquae cylindrum CB im- 

 motum tamdiu sustineant, quamdiu alterutrius vires non augentur no- 

 tabiliter. Utri ergo primum nova vis accesserit, is alterum vincens 

 aquae cylindrum a se removebit; et contra, utri accedens frigus ali- 

 quid virium detraxerit, is alteri cedens aquei cylindri pondere arctius 

 argebitur et comprimetur. Quod si contingat utrumque equali caloris 

 gradu in aere libero rarefieri, tunc superum CE, quippe copiosiorem, 

 vincere, et inferum BA cedere, necessum alicui videatur, quia tunc 

 partibus aequalibus singulis utriusque aeris aequalis vis expansiva per 

 rarefactionem accrescat, tales autem partes plures habeat aer superior 

 quam inferior. Verum cum contrarium nunc accidat, ratio videtur e 

 praecedanea majore aeris AB condensatione petenda." Page 54. 



In an appendix to this work, Sturmius goes on to discuss the proper- 

 ties of his thermometer, and he mentions that the Dutch artists, in place 

 of agglutinating the ball E to the stem at D v leave an opening at A, 

 which is afterwards hermetically sealed. He then mentions an experi- 

 ment, in which he muffles up the lower ball A, and exposes E to the 

 action of the solar rays. The liquid then descended, as the air in the 

 sphere DE became warmer. " In quo meo ratiocinio penitus confirmor 

 ipso momento, dum hoc ipsum thermometrum meurn, de quo hie ago, in- 

 voluta prius mucciuio sphaerula inferiore A, ita fenestra? admoveo ut sola 

 superior a meridiani solis radiis feriatur, videoque nunc liquorem sensim 



