242 PHILOSOPHICAL TRANSACTIONS. [aNNO I746. 



Of an Hygrometer made of a Deal Rod. By Mr. William Arderon, F. R, S. 



N°480, p. 184. 



Mr. A. perceived common deal expanded itself very much laterally, or across 

 the grain : and this he imagined, if properly used, might show the different de- 

 grees of moisture or dryness in the air. These thoughts set him on searching 

 the Philos. Trans, to see if any ingenious person had recorded his opinion on this 

 subject : and he found in N° 127, that an anonymous author had made several 

 attempts to construct hygrometers of deal boards ; and again, N° 1 29, that Mr. 

 J. Coniers had added some improvements to it; but as the method taken by these 

 two gentlemen seemed liable to some objections, he determined to make a trial 

 on a plan and form entirely different from theirs; and has been so fortunate as to 

 succeed greatly beyond his expectations. 



His way was thus : he procured a piece of coarse deal board ; mostly of sap. 

 From this he sawed 7 pieces across the grain, 10 inches long and an inch broad; 

 and as the board was just an inch in thickness, he consequently obtained 7 

 parallelopipeds of an inch square each. 



These 7 pieces of deal he joined together, lengthwise, with strong glue ; which 

 made a square rod of 70 inches long. He found it necessary to place these small 

 pieces in such a manner, when he glued them together, in respect to their 

 grain, as is represented in the 2 figures following, to prevent their forming them- 

 selves into a sort of curve; which they naturally do, if they are placed ^11 the 

 same way ; and he found himself obliged to fix the rod in such a number of 

 brackets as appear in the drawings, in order to keep it straight. 



He placed this rod at first perpendicular to the horizon, between 2 pieces of 

 wogd of the same thickness, and nailed against the ceiling of his room ; but then 

 he had one side only exposed to the air : however it acted tolerably well, which 

 encouraged him to try to make it more perfect; as you will find delineated, fig. 1 

 and 2, pi. 6. 



Both these deal rods were placed against the ceiling of the room with brackets, 

 and were buttoned down into square mortises in each bracket, with small pieces 

 of deal, that fitted their tops exactly. Thus all their 4 sides became exposed to 

 the air ; and the only difference between them was, the increasing the effect of 

 their variation by 2 different methods. 



To the rod at fig. 1, he added 2 levers : the first of which abd had its shorter 

 end AB but 3 inches in length, and its longer bd 12; consequently the end d 

 moved through 4 times the space that the end a did. The second lever efg he 

 fixed to act with the former. The shorter end ef of this lever was 3 inches, and 

 the longer end fg, 43 inches; by which the effect of the other was increased 13 

 times, and that of the deal rod 60 times. So that if the rod lengthens but -rV of 



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