li' 



M. MELLONI ON THE FREE TRANSMISSION 



tlifi degrees to the forces was perceptible as far as the twentieth degree 

 of the scale, I have attentively observed the passage of the index through 

 every 4°, by commencing with this jjosition and continuing my obser- 

 vations as far as the forty-fourth degree. There I stopped ; for my ex- 

 periments on calorific transmission were to be confined to radiations 

 considerably weakened by distance. 



The arcs passed once in virtue of the forces acting on the system of 

 the needles at diflerent points of their course are in the following ratios 

 to one another: 



The arc comprised between 



20° and 24° is equivalent to 5°*12, commencing at zero. 



24 — 28 6 -44 



28 — 32 8 -00 



32 — 36 9-92 



36 — 40 12 -44 



40 — 44 19-04 



Each number in the third column represents the mean of eight obser- 

 vations, which agreed with one another as exactly as could be expected 

 from the nature of the instrument. Often equal, sometimes differing 

 by 0°*5, their greatest disagreement never exceeded 1°. A better proof 

 cannot be given of the exactness of the method. 



The linear construction of these results, which gives a very regular 

 curve convex towards the axis of the a;es, has enabled me to obtain the 

 values of the intermediate forces, degree by degree, from 20° to 45°. 

 By connecting them with the fundamental observations, I have formed 

 the following: table of the intensities : 



The use of a table requires no explanations. All the forces are re- 

 ferred to that wh'ch makes the index describe the first degree of the 

 scale. The values corresponding with the first twenty degrees are not 

 exhibited in it ; for through the whole extent of this arc the number 

 representing the force is equal to the number of degrees contained in 

 the arc passed over by the index. Thus, for instance, when we look 



