A work of this character possesses equal merit with one entirely completed before the death of the author. As a rule such works have not had the ad vantage of the final perusal and correction by the author. Such has not, however, been the case in the present. Instance, for the following work by the late George M. Hopkins, was completed before his death. Tl ere is no doubt, however, that this volume will come as a surprise to thousands who have closely followed Mr. Hopkins' work, and who have enjoyed making the many experiments described by him. The present volume contains much matter which has never before appeared in print, and some articles which have al ready been published in the Scientific American. The object of the work is to furnish food for thought to the amateur, and to give him suggestions whereby he may pass many pleasant hours in his work-shop. Mr. Hop kins was an expert mechanic. One of his chief pleas ures was to make experiments at'his home in his well equipped work-shop and laboratory, and the work described in the present volume is nearly all the result of experiments made by him during such idle hours. It has been the intent of the author to make the present.