In the following year, 1852, Channing and Farmer invented the fire-alarm telegraph, an important contribution to the safety of the Machine, though it did not come into general use for several years. In the same year, Fox Talbot made another of his epochal contributions to photography, by inventing a process by which photographic half-tones could be produced. In the following year, a process was invented for making from wood a pulp that was very valuable as the basis of making paper,--and Faraday made three important discoveries. These were the laws of electro-magnetic induction, the relations of the dielectric to the conducting bodies in electro-static induction, and the laws of electrolysis. These discoveries of Faraday were all inventions, in the sense in which the word invention is used in this book. Each one was the outcome of a series of careful and mathematically guided experiments, and the outgrowth of an idea. In the following year, Melhuish invented photographic roll films, and Herman invented the rock drill. The latter invention has been of the utmost practical value in blasting operations of all kinds, and must be regarded as a very distinct addition to the Machine. In the same year, appeared the Smith & Wesson revolver; not a great invention, but an improvement in many ways over Colt's; Mr. A. B. Wilson brought out his four-motion feed for sewing-machines, and R. A. Tilghman invented his process for decomposing fats by hot steam. In the following year (1855), Lundstrom made the highly important invention of safety matches. When one reflects (as every one must at times) how great and absolutely irretrievable are the losses caused by fire each year, how the amount of possible destruction grows each year exactly as fast as the Machine grows, and realizes how large a fire many a small match has caused, he feels inclined to give a mental salute to Mr. Lundstrom of Sweden. In the same year, iron-clad floating batteries were used in the Crimean War. This was not the first time that iron-clad vessels had been employed, for vessels protected on the sides with sheets of iron and copper had been used by the Coreans in their victorious war against the Japanese about three hundred years before; but it was the first time that such vessels had appeared in Europe. Cocaine was invented the same year, and one of the most valuable anæsthetics yet known was then produced.