INTRODUCTION. XXXIX 



causes of similar phenomena. Consequently, the committee pro- 

 poses to the Academy to give its approbation to the labors of Mr. 

 Espy, and to solicit him to continue his researches, and especially 

 to try to ascertain the influence which electricity exerts in these 

 great phenomena, of which a complete theory will be one of the 

 most precious acquisitions of modern science. 

 The conclusions of this report are adopted. 



NOTE. 



I have stated in the Synopsis, that islands, with high mountains in them, 

 are more likely to have rains from sea breezes, than those without moun- 

 tains. The following facts go to confirm that position, and they will 

 be easily understood from the theory, without further explanation. Cer- 

 tainly they are not to be explained by any supposed attraction of mountains 

 for clouds, as is asserted by the author of the American Almanack, and by 

 many higher authorities. The facts, indeed, which Mr. Borden gives, prove 

 that the cloud is not attracted to the mountain, but formed there. 



Dr. Campbell, of Lancaster, England, observes, " that the influence of hills, 

 in attracting clouds, is nowhere more conspicuous than at Kendall ; that one 

 third more rain falls at Kendall than at Lancaster, a distance of only twenty 

 miles, and that it is by no means unusual to see from the church yard at Lan- 

 caster, the hills about Kendall enveloped in thick clouds, while the sky at 

 the Lancaster side of Farlton Kriott appears perfectly clear. And Dr. Gar- 

 nett says, the summer of 1792 was remarkably dry in Yorkshire, and all the 

 eastern side of the English Appennine was burnt up for want of rain ; while, 

 on the western, they had plenty of rain and abundant grass." [Transac. of 

 Royal Irish Acad., vol. xvii. p. 224. 



"That the mist should remain so nearly stationary on the top of Table Hill, 

 while the south east wind continues, is not surprising, considering the height 

 of the hill, 3582 feet above the level of the sea, its precipitous sides, and the 

 extensive surface of its top ; nor is it strange that it should rarely descend, 

 except when the wind blows hard, taking into account the situation of the 

 ground beneath, sheltered and warm, and the site of a large town, from 

 which a current of hot air must constantly be rising." [Mr. John Davy. 

 Tilloch's Magazine, vol. li. p. 35. 



" The air on the summit, which rises to the height of 3582 feet above the 

 level of Table Bay, in the clear weather of winter, and in the shade, is gene- 

 rally about fifteen degrees of Fahrenheit's scale lower than in Cape Town. 

 In the summer season the difference is much greater, when that well known 

 appearance of the fleecy cloud, not inaptly called the table cloth, envelopes 

 the summit of the mountain. In the heat of the summer season, when the 

 south east monsoon blows strong at sea, the water taken up by evaporation 

 is borne in the air to the continental mountains, where, being condensed, it 

 rests on their summits in the form of a thick cloud. This cloud, and a low 

 dense bank of fog on the sea, are the precursors of a similar but lighter 

 fleece on the Table Mountain, and of a strong gale of wind in Cape Town 

 from the south east. These effects may be thus accounted for : The con- 

 densed air on the summit of the mountains of the continent, rushes, by its 

 superior gravity, towards the more rarefied atmosphere over the isthmus, 

 and the vapor it contains is there taken up and held invisible, or in transpa- 

 rent solution. From hence it is carried by the south east winds towards the 

 Table and its neighboring mountains, where, by condensation from decreased 

 temperature and concussion, the air is no longer capable of holding the va- 

 por with which it was loaded, but is obliged to let it go. The atmosphere 



