280 



Dr. T. R. Robinson on the Determination of [Apr. 4, 



the morphological representative of the mid gut, and that the liver 

 really arises as a diverticulum from it. 



Four varieties of embryos, taken from animals answering the 

 description of G. oestroides, are described ; but as it was found impos- 

 sible to make out any differences in the adults, the question whether 

 these varieties represent distinct species or polymorphic forms is left 

 undecided. 



II. " On the Determination of the Constants of the Cup Anemo- 

 meter by Experiments with a Whirling Machine." By 

 the Rev. T. R. Robinson, D.D., F.R.S., &c. Received March 

 14, 1878. 



(Abstract.) 



In his description of the cup anemometer (Transactions Royal 

 Irish Academy, Vol. XXII), Dr. Robinson inferred from experiments 

 on a very limited scale with Robins' whirling machine, that the 

 ultimate ratio of the wind's velocity to that of the centre of the cups 

 = 3. Some recent experiments by M. Dohrandt show that this number 

 is too great ; but as some of the details appeared objectionable, and as 

 they did not include all the necessary data for determining the con- 

 stants, the author was desirous of repeating them. He was enabled to 

 do this by a liberal grant from the Royal Society, and the results are 

 given in this paper. 



After describing the apparatus and the locality in which it was esta- 

 blished, he proceeds to explain the conditions of an anemometer's action. 

 Considering only two opposite cups, and supposing them in motion, 

 the pressure on the concave surface is as that surface and the square of 

 the resultant of the wind's velocity V and v, that of the anemometer, 

 and as a, the pressure of an unit V on the cup normal to the arm. 



This is opposed, 1. By the pressure of a similar resultant on the 

 convex surfaces, and a, another coefficient, also normal to the arm, but 

 quits different from a; 2. By various resistances depending on v 2 ; and 

 3. By the friction of the machine estimated at the centres of the 

 cups. 



a and a are functions of V, v, and 0, the angle which the wind makes 

 with the arm, but it is impossible to determine them a priori in the 

 present state of hydrodynamics. It is, however, obvious that if V be 

 constant, the mean values of v, a, and a through one revolution will 

 soon also become constant, and as the mean impelling and resisting 

 forces balance each other, the condition of permanent motion is ex- 

 pressed by an equation of the form aV 2 — 2fiVv - 7V 2 — F = ; or 



Y* — 2xYv—yv i —-=0 (I), which, if the constants are known, gives 



a 



