Mea/urement of a Bafion Hounflow-Heath. 43 ^ 



'Can be little doubt, that de^il rods will be unlverfally reje8:ed by- 

 other countries, in any meafurements they may have occafioii- 

 to make ia future. 



About the loth of July, two rods, one of Nevv-Ei>gknd 

 and the other of Riga deal, being meafured by the fixed points 

 in the great plank in Mr. Ramsden's fhop, and having each 

 two brafs pins driven into them at the diilance of twenty feefj' 

 were laid on the top of the houfe, w^iere they remained until 

 the 26th, the weather, for the greater part of the time, having 

 been very wet. They were then taken down, and being, by 

 means of the long beam compares, compared with the mea- 

 fures on'the plank, the New-England rod was found to have 

 lengthened 0,03 1 inch, and the Riga rod 0.041 inch. By which 

 experiment tl^e ■fa<^ feems to be eftabliflied, that Riga red- 

 wood, notwithftanding the quantity of turpentine which it 

 contains, is' m-ore fufceptible of the effedls of moifture than 

 New-England, white wowl. Mr. Ramsden likewife finds, 

 that the great plank fo often mentioned, fuffers, in ordinarry 

 fummer weather, an alternate expanfion and contraction, 

 amounting at a medium to 0.0041 of an inch every day : that 

 is to fay, if the diftance between the twrenty-feet brafs points 

 be meafured from the fcale, by means of the beam compafles, 

 in the evening, it is found to have lengthened next morning 

 0.0041 of an inch, by the humidity of the intervening night. 

 In the courfe of the following day it contrads again to its for- 

 mer length, and fo on. Mr. Ramsden has often obfervcd 

 this alternate change in the deal plank ; but it was particularly 

 on the I ith and 1 2th of Auguft, that the quantity was a(3:ually 

 meafured. It will readily be underftood, that any difference of 

 temperature which might have happened in the brafs fcale, at 



the 



