THE MIRAGE. 253 



tended horizontall}^ the space between, tlie masts being 

 considerable, and each column of sails quite distinct. The 

 jibs were indistinctly erect and inverted alternately, giving 

 some appearance of a combination of images, but there was 

 no appearance of a hull. The vessels were some miles 

 distant from us probably hull-down. 



The temperature of the surface water varies much 

 amongst the Mingan islands. Several rivers empty them- 

 selves into the sea at this place, the waters of which, in 

 calms, float on its surface, which thus is sometimes several 

 degrees warmer than the water at the depth of a few inches. 

 A moderate current of air, which, amongst small islands is 

 often partial, sometimes, by agitating the water at one place, 

 renders the surface there cold, whilst it continues warm 

 in the place sheltered from the wind. We have, hence, 

 occasionally, strange combinations of mirage. On the 16th 

 and 17th of July, shortly before the double images of the 

 Peroquet were observed, the islands to the eastward of the 

 harbour had their extremities apparently projecting in the 

 air, as is usual in that species of mirage which depends on 

 the temperature of the surface being higher than that of 

 the air. The horizon on this side was low and near ; a rock 

 three miles distant, seemed above it. As the breeze sprung 

 up from the S. W. the horizon receded beyond this rock, 

 and the islands generally appeared to have flattened tops, 

 shomng the mirage of the opposite kind. But the ex- 

 treme points of the most distant island seemed still in 



