With the different champagne houses the mode of bottling the wine, which may take place any time between April and August, varies in some measure, still the _tirage_, as this operation is called, is ordinarily effected as follows:--The wine is emptied from the casks into vats or tuns of varying capacity, whence it flows through pipes into oblong reservoirs, each provided with a row of syphon taps, on to which the bottles are slipped, and from which the wine ceases to flow directly the bottles become filled. Men or lads remove the full bottles, replacing them by empty ones, while other hands convey them to the corkers, whose guillotine machines are incessantly in motion; next the _agrafeurs_ secure the corks by means of an iron staple, termed an agrafe; and then the bottles are conveyed either to a capacious apartment aboveground, known as a cellier, or to a cool cellar, according to the number of atmospheres the wine may indicate. It should be explained that air compressed to half its volume acquires twice its ordinary force, and to a quarter of its volume quadruple this force--hence the phrase of two, four, or more atmospheres. The exact degree of pressure is readily ascertained by means of a manometer, an instrument resembling a pressure gauge, with a hollow screw at the base which is driven through the cork of the bottle. A pressure of 5¾ atmospheres constitutes what is styled a “grand mousseux,” and the wine exhibiting it may be safely conveyed to the coolest subterranean depths, for no doubt need be entertained as to its future effervescent properties. Should the pressure, however, scarcely exceed 4 atmospheres, it is advisable to keep the wine in a cellier aboveground that it may more rapidly acquire the requisite sparkling qualities. If fewer than 4 atmospheres are indicated it would be necessary to pour the wine back into the casks again, and add a certain amount of cane sugar to it, but such an eventuality very rarely happens, thanks to the scientific formulas and apparatus which enable the degree of pressure the wine will show to be determined beforehand to a nicety. Still mistakes are sometimes made, and there are instances where charcoal fires have had to be lighted in the cellars to encourage the effervescence to develop itself.