﻿4:66 O. S. Sargent — Journey of Andre Michaux. 



rors, or yielding of the cement, is nil and is not to be appre- 

 hended, since the fixed mirror is a fiducial mark for the mova- 

 ble mirror. In the above work we do not indicate the amount 

 of permanent torsion left in each wire after the experiment is 

 finished. Though an important desideratum, it does not fall 

 within the scope of this paper. The effect of temperature on 

 twisted systems of pairs of identical steel wires we shall proba- 

 bly investigate later and then discuss the amount of detorsion 

 due to annealing at stated temperatures and times. The soft 

 ends introduce no serious error because soft steel is more vis- 

 cous than hard steel. The amount of twist registered is that 

 between the upper and lower points of attachment. The in- 

 cluded wires must be of uniform hardness. 



The fact that an effect of the bitilar and flexural components 

 is wholly absent in these results is proved by table 13A, in 

 which the curve for r+b+f is followed without break of con- 

 tinuity by the curve r~b — ■/,' and the total curve is practically 

 identical with the locus for table 13. It is proved, moreover, 

 by tables I, 2, in which couples of glass-hard wires show no 

 greater difference than is at once attributable to unavoidable 

 differences of hardness ; and by table 34, in which v+b+f and 

 r—b—f produce practically identical zero-effects on two soft 

 wires. It is generally proved by the distribution of the 50 

 rods examined in a diagram of viscosity conformably with the 

 respective tempers of the rods. If a couple of one hard and 

 one soft rod possessed a smaller total of viscosity than a couple 

 of two hard rods, then the bi filar and flexural couples might 

 produce an effect in the former case and not in the latter. The 

 absence of all effect in the case of two soft rods as well as in 

 the case of two hard rods shows that the discrepancy in ques- 

 tion is nil. The important bearing of this result will be indi- 

 cated below. 



[To be concluded.] 



Art. LIY. — Some Remarks upon the Journey of Andre Michaux 

 to the high Mountains of Carolina, in December, 1788, in a Let- 

 ter addressed to Professor Asa Gray ; by C. S. Sakgent. 



Having recently returned from a somewhat extended ex- 

 cursion through that portion of the mountain region of North 

 and South Carolina which lies about the head waters of the 

 Savannah Eiver, — the scene, I have reason to believe, of Andre' 

 Michaux's perilous and interesting mountain journey made in 

 the winter of 1788-89, and which, so far as I can learn, has 

 not been visited again until this year by a botanical traveler, 



