SS4 M. Arago 07h the T/iermometrkal State 



no mistake in these two authors, nor in the designation of the kind 

 of tree, nor respecting the localities ; if it be truly of the plains, 

 and not the mountains, they intended to speak ; then, the an- 

 cient climate of Rome, we perceive, should have been greatly 

 ameliorated with the course of time. To a temperature but 

 little inferior to that of Paris, must have succeeded one agreeing 

 with that of Perpignan. 



The idea that some error must have crept into the passages 

 to which we have just alluded, is confirmed by the circumstance, 

 that the latter of these authors, after having spoken of the beech, 

 says also, that the laurel and the myrtle grow in the plain of 

 Rome. But this supposes a mean temperature of at lest 55" 4' 

 or 57° 2'.* This brings us back to numbers, and though it be 

 but to the lowest limits where these shrubs grow, yet it is much 

 Jess removed fVom the real temperature. Let us, with Pliny, add, 

 that, in his time, the laurel and the myrtle throve in Mid-Italy, 

 even at some elevation upon the sides of the mountains. Let us 

 also remark, according to the testimony of all travellers, that 

 these plants do not, in these times, reach a higher habitat than 

 1200 feet; and from this coincidence, we may without hesitation 

 conclude, that ancient Rome cannot possibly be colder than mo- 

 dern Rome. 



Is it hotter ? A statement of the younger Pliny seems to lead 

 us to a negative response. In his letter to Apollinarius (lib. vi. 

 let. 6) he says of a country-residence situated in Tuscany,'^" There 

 are laurels. If they sometimes die, it is not more frequently 

 than in the neighbourhood of Rome," Thus laurels were some- 

 times killed in the environs of Rome ; hence the mean ordinary 

 temperature of this city ought not to be much elevated above 



• These limits of temperature are true only in regard to continental climates. 

 In islands, especially where the west winds, almost constant, passing over the 

 sea, render the winter extremely mild, the myrtle can live with a mean tem- 

 perature, far below 55° 4'. This plant, for example, thrives most wonderfully 

 on the shores of Glenarm in Ireland, in the latitude of 55°. But this happens 

 only because in such situations frost is scarcely known. It is because in them 

 the winter is milder than in Italy. But what is gained in such situations in 

 winter, is more than lost in summer. Thus, the grape does not ripen on the 

 sides of Glenarm. I refer such as are solicitous of studying the differences 

 which continental and maritime regions present as to the diffusion, throughout 

 the season, of the same annual heat, to the excellent Memoir of M. de Hum- 

 boldt on Isothermal Lines, ^laali . 



