82 DR HUGH ROBERT MILL ON THE 



at Inveraray. — These are the curves of greatest slope (12°*l) observed in Loch Fyne, and 

 represent the maximum heating effect. They are the nearest approaches to simple positive 

 paraboloids, and bear every evidence of being due to surface heat being propagated uni- 

 formly downward. Omitting the superficial fathom, which showed some cooling on the 

 27th, the upper layer of water showed well-marked heating down to 25 fathoms, and below 

 that depth a possible slight cooling, although the temperature was probably the same on 

 both occasions in the lower half. On the whole, the result of the interval of two days was 

 a rise of o, 2 in temperature. The 25th was a bright, warm day (air-temperature 62°7 at 

 time of observation, 10 h 0), with a light, southerly breeze. The weather on the 27th was 

 similar, though the ah- was cooler (57°'0 at the time of observation, I7 h 20), and the breeze 

 rather stronger. The gain of temperature for the first 20 fathoms may be put down as 

 0°"5 ; and as there were 3G hours of daylight and 19^ hours of darkness between the 

 observations, on the hypothesis of equal rates of gain aud loss of heat (see p. 58), the 

 effect of solar radiation and contact with warm air was to raise the temperature at the 

 rate of 0°'03 per hour to the depth of 20 fathoms, or 0°*012 per hour for the whole depth. 

 These are much smaller values than were obtained in similar cases of double observations 

 at a short interval of time at Skate Island, and equally valueless. Observations at Inveraray 

 were made by me from a rowing boat on 26th August and 3rd September 1889, Nos. 27 and 

 28 (fig. 35, Plate XXIX.). August 26th was calm, with overcast sky, and air-temperature 

 56° when the observation was taken at ll h 30. The tide was about high- water. In the 

 afternoon the weather became squally. The intervening week was warm, with light breezes 

 and little rain, except on the 2nd September, when a strong easterly breeze was blowing. 

 On the 3rd the sky was overcast, the weather calm and hazy, with a very light air from 

 the south-east, and the tide at the time of observation was within an hour of low-water. 

 The result of the week's warm weather was a rise in the mean temperature of the 

 sounding from 48°*1 to 48° '6. The two curves crossed at 10 fathoms, the upper layer 

 having cooled about 0°*7 on the average, while the 50 fathoms beneath had been warmed 

 up almost uniformly by o, 4. This plainly points to a considerable mixing of the water 

 in the interval, either by wind or tide, or both. No salinity observations were made. 

 On the first occasion the temperature gradient was exceptionally uniform from surface 

 to bottom, the curve being between a straight line and a simple paraboloid ; but on the 

 second occasion the gradient of the first 20 fathoms had been greatly reduced (clear 

 evidence of mixing), that of the lower 30 fathoms was unchanged, and the intermediate 

 10-fathom zone showed a marked accentuation, the curve having become a compound of 

 two paraboloids. 



Cross Section at Inveraray. — A cross section of Loch Fyne at Inveraray, from the 

 usual observing station to Inveraray pier, was made in the autumn of 1889 on two 

 occasions, August 26th and September 3rd. The isotherms were practically parallel and 

 horizontal in both cases, although in the interval there had been strong winds. Both 

 the days of observation were calm. 



Seasonal Variations. — The seasonal variations of vertical temperature in the deepest 



