A Companion to the Scientific Dialogues; Or, The Tutor's Assistant and Pupil's Manual in Natural and Experimental Philosophy:: Containing a Complete Set of Questions, and Other Exercises, for the Examination of Pupils in the Six Volumes of Scientific Dialogues, and Forming a Seventh Volume of that Work. To which is Added, a Compendium of the Principal Facts Under Each Department of Science. Published at the Request of Many Persons Engaged in the Education of the Young, Volume 7