124

HISTORY OF ENGINEERING.

Book I.

species of cavity, and acquired a considerable quantity of heat before the water enteredthem. Each of the chambers was within the walls, 49 feet 6 inches long, 27 feet 6 incheswide, and about 30 feet high; the number of superficial feet of the bottom of the chamberswas 38,115, allowing 30 feet for the mean height; the quantity of water contained inthe lower rooms amounted to 1,143,450 cubic feet, and it must be supposed that the upperrooms contained an equal quantity of water; consequently, if we give to each bather 8 cubicfeet of warm water, supposing that the water preserved its heat for half an hour, sufficienttime for a person to bathe, 18,000 persons consumed 144,000 cubic feet of warm water;according to this calculation, there was for the space of three hours, or till five o’clockin the evening, a sufficient quantity of water in the therm® for 108,000 persons; itmust, however, be acknowledged that the water cooled gradually in flowing from theupper rooms. The ancients do not inform us how they discovered the method of heatingsuch large volumes of water, nor do we know whether it was an invention of the Romansor Orientals. "We may reasonably suppose that it does not date further back than the timeof Augustus, as Dion Cassius informs us, that it was in his reign M®cenas built the firstwarm bath for swimming.

This, or some other similar method, must have been adopted in the tliermes of theRomans. It is evident that the vases described by Vitruvius would have been inadequateto furnish water to those vast buildings which Ammianus Marcellinus compares toprovinces ; but they were used in private baths, as we shall relate.

The water for the baths, says Vitruvius , was heated by means of three copper vessels,so arranged that it flowed from one into the other ; one was called the caldarium, theother the tepidarium, and the third the frigidarium; these vases were placed so that the

Fig. 132.

CALDARIUM.

FRIGIDARIUM.

TEPIDARIUM.

one which contained the warm water received as much tepid water from the tepidarium, asthe latter did cold water ; thus the same quantity was constantly maintained.

“ It is not easy,” says the Marquis Galiani, “ to form a very correct idea of the situationof these vases on the furnace.” C®sare Cisarano and Caporali have figured them one over theother, or one within the other, placing the frigidarium on the tepidarium, and this on thecaldarium, which stood immediately over the furnace; but the great difficulty in thisarrangement is that ‘.he heat, by the tendency of the flame to ascend, would be more likelyto act upon the frigidarium. Perrault, on the contrary, places the three vases on a level,and imagines there must have been syphons to conduct the water from one vase to theother; but without a piston, or some other expedient, the water could not rise to descendagain. This Perrault does not explain. From what we can judge of the paintings in theancient baths of Titus, it would appear that the three vases were placed on three steps, sothat the bottom of the water in one is on a level with the opening of the other, whence it iseasy to understand how they can flow one into the other ; the Marquis Galiani, however, doesnot believe this to be the true arrangement, and imagines that it is made so in the picturemerely to convey a better idea of this transversion from one vessel to the other. Thefollowing are his conjectures on the subject. “ I think that these three vases are all on alevel, the caldarium immediately over the furnace, the tepidarium a little further off, so asto experience the reverberation of the fire, rather than the fire itself; the frigidarium stillmore removed, on a heap of masonry which the flames could not touch. There was in thebottom a tube of communication from one vase to the other. From the caldarium to thebaths was a pipe, whence by a tap the quantity of water required was drawn. Anotherpipe brought the water from the reservoir to the frigidarium, and maintained itself at thesame level. All the drawings hitherto given to illustrate the descriptions of Vitruvius appear to require the superintendence of a servant to effect the transversion.” Neverthelessthis author leaves us to understand, that the operation was effected by itself, and without