182 



Retrospective Criticism, 



posited; an "explanation" which not only explains the fact 

 itself, but explains away the incorrect description of a " sub- 

 sidence." Cuvier and Brongniart state (p. 328.) that they 

 saw and copied the circumstance, as it was discovered by 

 M. Langlois, whilst digging a well in the garden of Madame 

 Fourcroy; and that the workmen ceased labour till they 

 could arrive at the spot. But I very much doubt whether 

 they discontinued working altogether, in order for Mr. Mog- 

 gridge to commence his "late researches" ten years after- 

 wards; and whether he ever became acquainted with this 

 " singular instance of subsidence!" except in the pages of his pre- 

 decessors. If so, this instance is very singular indeed, and 

 his " late researches" quite remarkable ! — W. B. Clarke. 

 Parhstone, near Poole, Dec. 22. 1832. 



The Pain Gauge or Pluviometer (Vol. V. p. 769.), and Pain 

 Gauges generally. — An objection to the rain gauge proposed 

 Vol. V. p. 769., and to all rain gauges withjoats, is, that they 

 do not measure the rain which is balancing the weight of the 

 float and rod. It is obvious, on look- 

 ing at the figure [we repeat the cut 

 Jig. 19.], that a good deal of rain 

 will fall before the float and rod are 

 raised from the bottom of the gauge. 

 Of course, in graduating the rod, an 

 allowance might be made for this ; 

 but, nevertheless, if only a small 

 quantity fell after each emptying of 

 the gauge, insufficient to raise the 

 float, it would not be indicated at all 

 .:5^ by the proposed gauge. I should 

 & prefer to dispense with the float and 

 rod, and measure the rain into a glass jar or tube, graduated 

 into cubic inches and tenths, and divide the amount by the 

 area of the funnel, which will give the rain on each square 

 inch of its surface. The funnel should have a raised edge, 

 or, in high winds, part of the rain may be blown out of it. 



The stopcock may be left 



uz 



20 



out, and a good cork sub- 

 stituted, and the whole 

 constructed like Jig. 20. 

 which is a box with top 

 10 in. square, the funnel 

 about 1 in. below its edge, 

 and on the side a short tube 

 for removing the water, 

 with cork or stopcock. 

 Suppose you have found 17*8 in. of rain in the gauge, the area 



