One of the principal of these, considering throughout the purpose of the structure, is, perhaps, the uninterrupted view of the interior which the spectator may obtain from any point of the building--a matter of great importance to the general grandeur of its effect. From the galleries more particularly, which will be less obstructed by large objects, the eye of the spectator will be able to range from end to end of the vast edifice; while the transparency of the material used for the roof allows every object to be brilliantly illuminated. The slender lines of the supports, though they serve to sustain a protecting covering, scarcely interrupt the view of the objects protected, and the absence of any fixed divisions or partitions enables all the articles exhibited to be so arranged as to suit the peculiar requirements of each particular class; while the ample space between the supports has admitted of the formation of large open avenues for the free passage of visitors, who may thus reach as readily the remotest corners of the building as those situated near the entrances; and whenever the visitor may find himself fatigued by the labour of sight-seeing, he will be sure to find himself near one of the numerous exit-doors, whereby he may immediately free himself from the crowd of spectators. From the simplicity of the details of the construction, and their constant recurrence, it will be seen that so long as the ends of the building were left incomplete, its size could easily be limited or expanded, so as to include that precise amount of space which, up to the last moment when the point could be kept open, appeared most likely to be required. This simplicity of arrangement will also be found very advantageous in case the building is removed after the termination of its present temporary purpose; as the parts may be easily separated without much injury, and as readily re-erected, either as a whole, or even in many separate buildings, having the same arrangement of parts, without the same general form or appearance. It has been calculated that the passages remaining in the building, after deducting the space appropriated to the objects exhibited, will hold more than 100,000 persons; though it is not to be expected that half that number will be collected there at one time. The ventilation and supply of fresh air for so vast a throng was therefore a matter of the first importance; and the means already described for accomplishing this great object are so ample, that any inconvenience from oppressive heat or foul air can hardly be expected. The canvass with which the roof is covered will not only serve to modify the heat of the sun in the interior, but it is expected that if it be watered by the hose of engines, it may even reduce the temperature within to considerably below that of the external air. From his experience in glass-houses for horticultural purposes, Mr. Paxton speaks confidently on this point.