On Coverings for Cucumber Frames. 297 



the manner of thatch. The projecting ends of the two long 

 laths will serve as handles, whereby the covering may be 

 easily and expeditiously moved on and off the frame by two 

 persons, one at each end; nor will it be difficult for one 

 person to remove or to place it, if two be not at hand. If 

 the breadth of the frame exceed four feet, or perhaps if it 

 reach that measure, it will be expedient to make two cover- 

 ings, as they become weak and unwieldy if too large ; and 

 in cases where there is an extended range of frames or pits, 

 which will require a number of them, about three feet will 

 be the most convenient breadth. 



It will appear evident that with this covering there are two 

 principles which co-operate in maintaining heat with greater 

 effect than with mats, or any other covering in common use ; 

 namely the preventing of its escape, through communication 

 with the external cold, and of its absorption through the 

 creation of vapour. As to the first, it is generally known, 

 and confirmed by constant experience, that in a covering 

 composed of any of those substances which are much sub- 

 divided, the interstices between the fibres or non-continuous 

 parts being occupied by air, such as straw, hair or feathers, 

 interrupt the communication of heat in a greater degree than 

 those of a more compact texture, the weight and extent of 

 surface in both being equal. Mats and most other sub- 

 stances which are commonly used for this purpose, being 

 more compact than straw, any covering composed of them 

 that can be conveniently used, is much thinner, and conse- 

 quently the heat passing quickly through them by means of 

 the contact of their particles, flies off rapidly at the outer 

 side. Next, in consequence of the straw being arranged in 



