Scientific Lectures. 135 



there was only the simple coarse form of vegetation represented by 

 the fern of our day. This is buried up amid strata, oftentimes con- 

 taining only the faintest indications of their origin ; and yet cut into 

 thin slices, it tells us by its cellular structure that it came from the 

 plant-world. The hard coal that we burn, under the microscope, 

 reveals the same facts ; sometimes a leaf or a branch, occasionally a 

 whole tree, at other times rootlets are revealed ; and thus we learn of 

 the variety of plants from which we have stored up fov us that 

 element which is to us a source of heat and a source of light. I 

 never can think of this without reflecting upon the little seedlet. 

 Cut an almond in two, and we find a germ, and around it the starchy 

 granules which are to be the nutriment for it in its early develop- 

 ment. In its babyhood it is to be nourislied by that which is stored 

 around its most vital part. So God Almighty has arranged our 

 earth and fitted it for us ; fitted it for the great functions of our race, 

 and stored up that which give not only heat and light, but power. 

 When we reflect that every pound of coal that is burned in a minute 

 of time represents 300 horse-power ; and according to the estimate 

 of Tyndall, the amount of coal consumed by England alone repre- 

 sents the power of 800,000,000 horses, we get some idea of the 

 ancient forces that played upon this earth, and that have been stored 

 away for man's benefit. 



You are all familiar with the operation of burning coal, so that I 

 need not dwell upon the changes which heat efifects in it. Here is 

 a little specimen which was obtained from a vein a mile and a half 

 within the earth, and which now bears the marks of the bark of 

 the tree to which it belonged. Let us subject this coal to heat. 

 Placing it in the bowl of a tobacco-pipe, it gives ofi' oils and gases; 

 and after it is heated the gas creeping from the stem of the pipe may 

 be lighted, the coal giving us both heat and light. 



If you will look at this chart, it will help you to understand how 

 this gas is made. Here is a retort of iron, and here is a furnace. 

 When this retort is filled with coal, gases are evolved which rise in 

 this metal tube. N"ext to this another set of furnaces is placed, back 

 to back, on the same principle that two in a bed are warmer than 

 one. The gases and the vapor are partially condensed, and passed 

 into the hydraulic main, as it is termed, and then the gases descend 

 and ascend through these tubes, or coolers, which i:educes the tem- 

 perature of the gas. Then we have here a shower of water which 

 passes through the gas and washes out the impurities, and at the 



