64 PROCEEDmQS OP THE L^cc., 1868. 



permanent scale, in inches and parts, for hourly motion, and calculates the 

 corresponding values of semi-diameter and parallax, in order to avoid the labor 

 of dividing in every case the moon's hourly motion along its path into minutes 

 of time. I adopt a permanent scale of ten inches for the earth's radius, (which 

 fixes moon's semi-diameter also) compute the value on this scale for the hourly 

 motion of the moon in her orbit, from the horizontal parallax and hourly mo- 

 tions in R. A. and Dec, for each occultation, and adjust the instrument for 

 this varying quantity, by using a scale of equal parts for minutes of time, laid 

 down on an extensible sJieet. This sheet is of caoutchouc, and the scale is made 

 'oariaUe by extending tJie sfieet, imtil sixty minutes or one hour on the scale cor- 

 responds in length with the computed value of the hourly motion of the moon. 

 Two such scales might be used if the uniformity of the rate of extension of the 

 sheet could not be trusted throughout the required extent of the variation of 

 houiiy motion in different parts of the orbit. These scales, made of the vul- 

 canized caoutchouc obtainable at the date of the construction of the instrument, 

 have now lost their elasticity and must be replaced before I can again use the 

 instrument. 



These expedients are simple, and I make them known, as the adoption of 

 one or both may add to the efficiency of Mr. Hill's instrument, or similar in- 

 struments. I am not aware that any one had proposed them at the time I ap- 

 plied them to my instrument. I have heard that Mr. Adie of Edinburgh has 

 proposed something similar to the last to thermometer scales I beheve, but I 

 do not know the date of his proposal, nor whether it has been adopted in the 

 scales of any instruments. 



Mr. W. Wragg Smith read a continuation of his paper on " The 

 Fall of the Leaf, &c." * 



JANUABY llTH, 1869. 



The President in the Chair. 



Books jReceived. 



Franz GeseUius, M.D., Capillar-Bhit undefibrimrtes zur ^Trans- 

 fusion, 



* See Note, page 61. . _. - 



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