On the Theory of Newton's Rings. 451 



need scarcely be taken into consideration as any set-off against 

 a principle promising a gain of forty to one. 



The following additional demonstration of this principle 

 having been submitted to Mr. Walker, he requested that it 

 may be added as corroborative of his views. 



If the French experiment of the wedge form, represented by 

 fig. 3, were made only one foot deep, by two feet wide at the 

 base, that half of the prow below the centre line would cor- 

 rectly represent the plane AB, fig. 4 ; and if both were moved 

 horizontally with the velocity of ten feet per second, as from 

 AB to CD, the plane AB would just meet half the resistance 

 of the prow. 



Experiment has shown that the two square feet of base to 

 the prow, would, if the prow were absent, at that velocity re- 

 ceive 100 pounds resistance each, = 200 pounds; and that, 

 with the prow, the resistance would be T %ths of this, or 80 

 pounds. Thus one-half, or 40 pounds, would be the hori- 

 zontal resistance of the plane AB, moving ten feet per second, 

 which is equivalent to 400 pounds moved one foot per second. 



As the resistance varies as the squares of the velocities, if 

 the plane AB were placed horizontally, as represented by AE, 

 and then depressed in one second to DB (being one foot), each 

 of the ten square feet would only receive one pound of resist- 

 ance, and the whole would be ten pounds moved one foot per 

 second, which is just one-fortieth part of the power required 

 in the former case. Q. E. D. G. C. 



November 4, 1 850. 



LXII. On the Untenableness of the received Theory of 

 Newton's Rings. By E. Wilde*. 



A DESIRE to investigate the colours of thin plates more 

 -^*- closely induced me to have an instrument prepared, bv 

 which I am enabled actually to measure the diameters of the 

 coloured rings of Newton to the ten-thousandth part of an 

 English inch, and to attain by estimation an accuracy of one 

 hundred-thousandth of an inch ; the same instrument deter- 

 mines the approximation of the glasses to the millionth of an 

 inch. It is therefore capable of a greater degree of exactness 

 than even the spherometer of Biot. I will name it a gyrei- 

 dometer. 



Some years ago an instrument for the exhibition of New- 

 ton's rings was invented by Jericau in Sweden ; it was named 

 a gyreidoscope by its inventor. The instrument however 



* Translated from Poggendorff's Annalen, vol. Ixxx. p. 407, July 1850. 



2G2 



