352 Professor Forbes's Researches on Heat. 



is concave to the axis, or the Statical effect increases in a less ra- 

 tio than the Dynamical effect. The convexity of the one curve, 

 almost compensating the concavity of the other, the relation ob- 

 tained between the first impulsive arc and the calorific force, is 

 nearly linear. 



11. This will be best illustrated by comparing the true ratios 

 of the forces obtained from the above table, with the simple ratio 

 of the first deviations ; and to put it in greater evidence we shall 

 suppose a deviation of 20°, which is greater than we have ever 

 employed in these experiments. 



First Deviations compared. 



Ratio. 



Ratio of Intensities. 



20° and 1° 



.050 



049 



20—2 



.100 



.097 



20—4 



.200 



.191 



20—8 



.400 



.395 



20 — 12 



.600 



.593 



20 — 16 



.800 



.796 



Since, therefore, even in this case, we should never have an er- 

 ror amounting to a unit in the second decimal place, I have con- 

 tented myself in this paper with the employment of the simple 

 arithmetical ratio of the first arcs passed over. 



12. The construction of the table in Art. 8. was attended 

 with much more trouble than I anticipated. The relation be- 

 tween the Dynamical and Statical effects appears to depend up- 

 on circumstances very easily overlooked. Comparisons repeated 

 apparently under the same circumstances often differ very mate- 

 rially, relatively to the magnitude of the quantity sought, name- 

 ly, the difference of the two effects, which is always small. This 

 seems chiefly to depend upon the condition of the conducting 

 wire which has transmitted the electric current. It is well 

 known, that such wires retain for some time the molecular con- 

 dition, into which they have been thrown, by transmitting elec- 

 tricity, even after the current has ceased. This may be expected 

 perhaps to be even more strongly the case in electricity of small 



