Replij to Capt. Forman on the Theory of the Tides. 335 

 correct time, by merely observing that the enlightened part of 

 the moon 23' 30" must be near the end of the eclipse, since both 

 the time and the quantity of the enlightened part of the moon 

 continue augmenting; nevertheless, the time of this measure- 

 ment is 21'^ 0' 13",9, i.e. less than 21^ 20 45", which is evi- 

 dently absurd. This error of the text leaves no other alter- 

 native than to deduct the time, for which the observation is 

 calculated, from that of the full moon, which gives us 19 

 27' 28",8. Another evident error of the text is detected as 



"" "" Mean thne at Paris 21" 0' 13",9 according to the text. 

 Ibaguel5 50 54,9 



Longitude in time 5 9 19 



instead of 5 9 39 given in the text. 



Error 20" 



LXIII. Reply to Captain Fokman on the Theory of the Tides. 

 By Mr. Henry Russell. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen,- As I happen to have a particular veneration 

 for old theories when I consider new ones incapable ot ex- 

 ploding them, I shall, with your permission, reply to Captam 

 Forman's communication of last month, in which he so waimly 

 advocates the expansive theory of the tides. 



Surely it does not follow, because we admit the expansion ot 

 water, that therefore we must, without consideration, relinquish 

 our former theories of the tides ! No. Let us call ior the as- 

 sistance of expansion when we can no longer do wiUiout it, 

 and reject our present opinions when we discover their re en- 

 fi^n u mecessary, taking care, as far as we are able, to admit 

 no more causes \han art necessarily required to produce the 



^^As Captain Forman has proposed a box of marbles for my 

 instruction, I shall propose for him '-^ ^'f "^^l" -^y ;>^. .^'-y';;! '^^ 

 exneriment. Fill the box at one end with wheat and the 

 other with bran; of course we must consider the wheat the 

 ebb, and the bran the flow: on agitating the box the wheat 

 will descend, and consequently the bran will be eleva ed 



Captain Forman next mentions an immense syphon, the 

 existence of which of course I shall not argue; but, those wlio 



