544 Professm- Tyndall^ [June 4, 



by the force of the wind, and our carriages by animal power, than 

 to employ steam power for these purposes. We do not find it 

 desirable to wait for the bleaching of our calicoes by the sun's rays ; 

 and even the grinding of corn is no longer entirely confided to 

 wind and water power. 



in such cases, where contemporaneous natural agencies have been 

 superseded, we have almost invariably drawn upon that grand store 

 of force collected by the plants of bygone ages, and conserved in 

 our coal fields. It is the solar heat of a past epoch that furnishes 

 the power which we now utilise in our steam-engines. One im- 

 portant element in cheap production is time^ and it is precisely in 

 regard to this element, that we economically supersede, in the 

 above instances, the contemporary resources of nature. Now time 

 is also an important element in the natural production of food ; 

 and although it is true, that the amount of labour required for the 

 production of a given weight of food is not considerable, yet it is 

 nevertheless true that this weight requires a whole year for its pro- 

 duction. By the vital process of producing food we can only have 

 one harvest in each year. But if we were able to form that food 

 from its elements without vital agency, there would be nothing to 

 prevent us from obtaining a harvest every week ; and thus we might, 

 in the production of food, supersede the present vital agencies of 

 nature, as we have already done in other cases, by laying under 

 contribution the accumulated forces of past ages, which would thus 

 enable us to obtain in a small manufactory, and in a few days, 

 effects which can be realized from present natural agencies, only 

 when they are exerted upon vast areas of land, and through con- 

 siderable periods of time. 



[E. F.] 



WEEKLY EVENING MEETING, 



Friday, June 4. 



The Duke op Northumberland, K.G. F.R.S. President, 

 in the Chair. 



John Tyndall, Esq. F.R.S. 



PBOFESSOB OJP NATUKAL PHILOSOPHY, HOYAL INSTITCTION, 



On the Mer-de- Glace, 



A portion of a series of observations made upon the Mer-de-Glace 

 of Chamouni during the months of July and August last year 

 formed the basis of this discourse. 



