REMARKS ON GROWING PLANTS IN Gl.ASS CASES. 155 



In the opinion of Mr. Ward, it is owing to the " quiet state of the 

 atmosphere surrounding the plants enclosed in these cases that they 

 are enabled to bear the extremes of heat and cold to which they are 

 exposed in these long voyages." In proof of the former position he 

 refers to the well-known experiments of Fordyce and Blagden, who 

 were able to remain, for a short time, in a close room raised to the 

 temperature of 212°, or even 260°, Fahr. ; and in support of the 

 latter he appeals to the experience of Mr. King, who accompanied 

 Captain Back in his late expedition to the arctic regions. That 

 officer states that a difference of 10° or 80°, either from cold to heat, 

 or from heat to cold, did not suspend his usual avocations in the open 

 atmosphere when the air was perfectly still ; but, though the tem- 

 perature might be 40° higher, if it was accompanied with a stiff 

 breeze, he did not stir from home. In like manner Sir Edward 

 Parry found that a degree of cold sufficient to freeze mercury could 

 be more easily borne when the air was perfectly calm, than when, 

 with a stiff breeze, the temperature was 50= higher. " When the 

 cold was 40^ below freezing on the Fahr. scale," says Mr. Laing, 

 in his late " Tour in Sweden," " it was quite practicable to prosecute 

 the great cod-fishing in open boats in the Lafoden Isles within the 

 arctic circle. The calmness of the air which accompanies this ex- 

 treme cold is a kind of natural safeguard against its severity, the 

 abstraction of heat from our bodies being then much less rapid. 

 Such a hard winter," he adds, " is considered here a blessing next 

 to a good crop ; for the fisherman then gets out to sea, the landsman 

 gets in his timber out of the depths of the forest, and the inhabitants 

 of the most pathless districts obtain their supplies of grain, potatoes, 

 &c, at little cost of transport."— ( Tour in Sweden, p. 364.) 



The powerful and rapid operation of wind in lowering tempera- 

 ture was shown in an experiment of Dr. Heberden, recorded in the 

 « Philosophical Transactions " for 1826- He suspended a ther- 

 mometer, previously raised to 100 3 Fahr., in an atmosphere at 31°, 

 when a strong breeze prevailed, and in about half a minute the 

 mercurv fell not less than 48°; whilst in an atmosphere at 30\ but 

 without' any perceptible wind, the fall of the mercury, previously 

 raised, as before, to 100°, was only W in the same period of time. 

 These facts, which doubtless apply to vegetable as well as to other 

 bodies, due regard being had to differences in their conducting powers, 



