388 ON THE EFFECT OF COAL FIRES ON THE EYES. 



the tail, de, back, and abdomen are tightened and contracted, lest by 

 striking against the water, they should hinder the anticipation of the 

 tail, be. Now the tail being carried to g, and very much incurved 

 towards the head, a, and all the fins being expanded, the whole length, 

 bg, strikes with great velocity, and impels the lateral water like an 

 oar, by describing not a circular, but elliptical arc gd; by which motion 

 impelling the posterior water, and leaning against it, the fish must 

 necessarily move forwards from b towards a. In the second place, the 

 tail being anticipated, it finally strikes from h towards c ; by which 

 contrary motion, the preceding deviation from a straight course is 

 corrected, and, at the same time, the direct impulse of the fish from b 

 toward a, is doubled. And by this reasoning and method the progress 

 of fishes is effected in water. 



The same flexion of the tail easily performs the oflice of a rudder, 

 by bending its course either to the right or left. But the bifold fins 

 which exist at the extremity of the lower part of the belly, serve for 

 the motion towards the bottom. Because these fins, lying underneath 

 and exserting towards the tail, are expanded and erected, and perform 

 the office of an horizontal rudder, as the tail being depressed does in 

 birds. Therefore, the head of the fish must be inclined towards the 

 bottom : and the contrary for the motion upwards. The lateral fins, 

 or oblique flexupus wings, and elevated aboye, can discharge the same 

 office ; and also the tail of birds by which the course of the bird is 

 directed upwards, being raised up does the same. 



And perhaps, by the fins in the tail of fishes being inclined obliquely 

 upwards or downwards the same act may be executed ; which is con- 

 jectured from the circumstance, that fishes are directed upwards or 

 downwards in a moment, from a state of rest ; which rapid contortion 

 those small fins could riot effect, as the flexion of a rudder would be 

 unable to turn a ship that was at rest. 



ON THE EFFECT OF COAL FIRES UPON THE COLOUR OF 



THE EYES. 



BY THE REV. T. PRICE. ' 



IT is a remarkable fact, and no less so, as having remained so long 

 unnoticed, that in Britain the dark coloured eye is always found to 

 prevail in the neighbourhood of coal mines, and where coal is used as 

 the general fuel ; while, on the other hand, the light, or blue eye belongs 



