162 History of Mechanical Iiiventioius and 



The perches at Fahlun in Sweden, according to Linnaeus, 

 and those of a lake in Merionethshire in Wales, according to 

 Pennant, are of this strange variety ; a^d Sir W. W. Wynn, 

 Bart, the proprietor of this lake, sent Baron Cuvier some indi- 

 viduals of this kind, which are now in the Royal Museum. 

 This malformation Cuvier attribut,^s to the nature o^ the 

 waters tliey inhabit. 



In the lake of Geneva during winter, when the cold hinders 

 them from approaching the surface, it happens sometimes, 

 when fishing at a depth of 40 or 50 fathoms, that many perches 

 are seen floating at the surface of the water with the stomach 

 inflated and projecting from the mouth ; and these perish in a 

 few days if this be not perforated with a needle. This is oc- 

 casioned by the dilatation of the air in the swimming-vessel ; 

 but it never happens in places where the water is of less depth, 

 and of course where the contained air cannot be so much com- 

 pressed. The fishermen say, that if the fish be touched by 

 the fishing line at this depth, they experience this revulsion of 

 the stomach ; and in truth fear may be a sufficient cause for 

 the animal rising too rapidly to the surface. As M. Jurine 

 remarks, at 50 fathoms the fish is under the pressure of more 

 than eleven atmospheres ; and when this weight is instanta- 

 neously removed, the air is dilated in the vessel more quick- 

 ly than it can be absorbed. In this species, as in the greatest 

 part of the Acanthopterygious fishes, there is no outlet in this 

 vessel either towards the oesophagus or stomach. 



Art. XXV— history OF MECHANICAL INVENTIONS 

 AND OF PROCESSES AND MATERIALS USED IN 

 THE FINE AND USEFUL ARTS. 



1. Account of an Improved Air Pump, By the Reverend 

 John Macvicae, A. M. Lecturer on Natural Philosophy in 

 the University of St Andrews. Communicated by the 

 Author. 



The toleration of the scientific world for the many projects to 

 improve the air-pump which prove abortive shows that a want 

 is felt ; and as I have thought over the instrument occasion- 

 ally for several years, and despair of simplifying it farther, I 



