298 CHEMICAL COMBINATIONS 



state of thin air, should, by some extraordinary mechanism, by 

 bound up and imprisoned, in such vast stores, in the solid moun- 

 tains of the globe, be destined to pervade and refresh all na- 

 ture, in the form of water, and to beautify and adorn the earth 

 in the solid parts of animals and plants. But all nature is full 

 of similar wonders, and every step we advance in the study of 

 the principles of our art, we cannot fail to perceive the united 

 skill and bounty of the same great Contriver. 



2. It has been stated by some philosophers, that when the 

 leaves of plants are in a state of rest, their respiration is reduced 

 to its minimum point, and that it increases within certain limits, 

 as motion is communicated to them by the action of a current 

 of air. Now this may be perfectly correct, and very likely is 

 so ; although, under natural conditions, the suspension of respi- 

 ration has never been accurately ascertained. Various physiol- 

 ogists have attempted to discover the minimum of respiratory 

 suspension, under certain atmospheric conditions, but without 

 any satisfactory results. But it does not require the discovery 

 of this delicate point, to decide on the propriety or utility o 

 atmospheric motion. That a certain motion in the atmosphere 

 is beneficial, we know; but then, it becomes a question of degree. 

 We know that the gentle zephyr is favorable to vegetation, and, 

 even in a hot-house, we have some reason to suppose it is so, 

 under certain circumstances, and to a certain extent. Now it is 

 under the uncertain circumstances, and the uncertain extent to 

 which this practice is carried, that we have any objections ; for 

 such circumstances, and such indiscriminate abuse of the prac- 

 tice, we know to exist ; and hence the chemical effects of venti- 

 lation, in the majority of cases, instead of promoting respiration, 

 rather tend to prevent it, by depriving the atmosphere of the 

 principal element that nature has designed to carry on the work. 



The mechanical and chemical influences are intimately con- 

 nected with each other, so that to secure the chemical ad- 

 vantage of ventilation, I presume consists in maintaining the 

 proper equivalents of the atmosphere, which nature has deter- 

 mined as essential to the development of vegetation. If this 

 view be correct, the grand and important practical question 



