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being previously examined for radio-activity, and also the bottom being 

 tested. 



Top box, — 



Nitrogen, argon, &c. 



Oxygen 



Carbon-dioxide 

 Bottom box, — 



Nitrogen, argon, &c. 



Oxygen 



Carbon-dioxide 



Temperature of well, 12-7 C. 



The means of these are, — 



Top box, — 



Nitrogen, argon, &c. . . 16-82 



Oxygen . . . . 5-34 



Carbon-dioxide . . 1-80 



Bottom box, — 



Nitrogen, argon, &c. 



Oxygen 



Carbon-dioxide 



15-98 

 5-68 

 1-88 



As a check, the water of the Avon was examined, and the gas content 

 found as follows : — 



Nitrogen, argon, &c. 

 Oxygen 

 Carbon-dioxide . , 



Temperature, 11*4 C. 



C.c. per Litre 



at N.P.T. 

 , . 15-36 

 7-74 

 1-30 



which are just about ordinary saturation values at the temperature. 



From the above it appears that the gas content of these wells varies 

 within small limits, as we are of opinion that the different values obtained 

 in the several determinations of the same water are real, and are not to be 

 ascribed to errors. It also appears from the mean values that the efiect of 

 rippling is to diminish the nitrogen content and to increase the amount 

 of oxygen ; and, whilst the top box of the series at the hatchery contains 

 an excess of nitrogen over river values of 1-4 c.c. per litre, and of oxygen 

 a deficit of 2-4 c.c. per litre, at the bottom box these are altered to nitrogen 

 in excess 0-62, and oxygen in defect 1-06. 



As the cause of this part of these experiments was the pecvdiar mortality 

 to be found amongst trout confined close to a well, the facts regarding this 

 mortality may be briefly restated. 



Of trout confined near the Museum well, a very large proportion die 

 within a few days. Of those not dying, few escape what is known as " pop- 

 eye," a disease which manifests itself by a protrusion of the eyeball. This 

 disease has been ascribed by Marsh and Goreham to an excess of gas, chiefly 

 nitrogen, in the water. 



Of eggs hatched in the boxes we have examined at the hatchery a con- 

 siderable proportion die, and the mortality in the egg-state diminishes 

 rapidly over the series of boxes, of which the first and fifth have been ex- 

 amined for gas content. The figures relating to these were given previously. 



Blue Swelling. — This disease attacks the young trout in the yolk-sac 

 stage, and, like the three previously mentioned, its effects seem to fall off 



