I have had a long experience, both in lecturing myself and in assisting in the training of others to lecture and also to inform the uninstructed public by means of museum-labels and popular notes. It seems to me that there are a large number of men who, even though capable of expressing themselves clearly under usual circumstances, yet fail to do so when trying to expound or to teach, in consequence of three distinct faults, any one of which is enough to render their discourse or writing hopelessly obscure to “the man in the street.” These are, first, a kind of pride in using special terms and modes of expression which infatuates the lecturer or writer, and leads him, without reflection, to an attitude of mind expressed by saying, “That is the correct statement about this matter, short and true. If you don’t understand it, there are others who can. You can leave it alone; it is not worth my while to spend time and trouble to explain further; it is for you to give yourselves the trouble to find out what I mean.” The second fault is a real incapacity (which occurs in many learned men) to realise the state of mind of the uninstructed man, woman or child who eagerly desires to be instructed: this is want of imagination and want of sympathy. There is no cure for those who fail as teachers for either of these two reasons. The third fault is much more widely at work, and the most kindly sympathetic lecturers and writers--but more especially lecturers--often suffer from it and could easily amend their practice. It consists in the attempt to tell the audience or reader too much--vastly too much--in the limit of one hour, or within the space of a few lines or pages. This failure is well-nigh universal. I have heard a distinguished discoverer, an eloquent and able man, try to tell a completely ignorant audience in one hour the results of years of experiment and work by many men on the electrical currents observed in nerves. The audience did not know what is meant by an electrical current, nor anything about nerves, nor a single one of the technical terms necessarily used by the lecturer. The task was an impossible one. In six lectures it might have been accomplished, and great delight and increase of understanding afforded to the listeners instead of perplexity and a sense of their own incapacity and the hopeless obscurity of science. That, I am convinced, is the real trouble, viz., the attempt to tell too much in a short time, the failure by the lecturer to arrange his exposition in a series of well-considered, definite steps, each exciting the desire to know more, and each given sufficient time and experimental illustration or pictorial demonstration to lodge its meaning and value safely and soundly in the tender brain of the ignorant but willing listener. I am convinced that there is in very many lecturers a tendency to try to crowd and compress into one lecture what should occupy ten--if the willing and