§ 1. The passage of heat through matter has been mainly examined in reference to the diathermancy of solids, liquids, and gases to radiant heat, and to the conduction of contact-heat through solids and gases. The conduction of contact-heat through liquids forms a chapter in heat transference which has not hitherto received as much attention from experimental physicists as it merits. § 2. In the following pages I have the honor of submitting to the Royal Society certain experimental results and considerations to which I have been led during an investigation of this subject. These results are necessarily incomplete. The inquiry is fraught with very numerous and considerable experimental difficulties; but I venture to hope that such as the results are, they may be found useful to those who shall hereafter pursue the subject with greater skill and more perfect appliances.