Anna Tambour presents 


The virtuous medlar circle
thoroughly bletted
  A Dead-Guests-Can't-Say-No Featured Classic 
(including an experiment with the burning glass, that most boys have often tried)

by Sir Robert S. Ball


Suppose that you were able to endure any degree of heat, and that you had some way of setting out on a voyage to the sun. Take with you a wax candle, a leaden bullet, a penny, a poker, and a flint. Soon after you have started you find the warmth from the sun increasing, and the candle begins to get soft and melt away.  Still, on you go, and you notice that the leaden bullet gets hotter and hotter, until it becomes too hot to touch, and upwards the temperature continues to move, until at last the lead has melted, as the was had previously done.  However, you are still a very long way from the sun, and you have the penny, the poker, and the flint remaining.  As you approach closer to the luminary the heat is ever increasing, and at last you notice that the penny is beginning to get red-hot;  go still nearer, and it melts away, and follows the example of the bullet and the candle.  If you still press onwards, you find that the iron poker, which was red-hot when the penny melted, begins to get brighter and brighter, till at last it is brilliantsly white, and becomes so dazzling that you can hardly bear to look at it;  then melting commences, and the poker is changed into a liquid like the penny, the lead, and the wax.  Yet a little nearer you may carry the flint, which is now glowing with the same fervour which fused the poker, but at last the flint too will have melted.

You will ask, how do we learn all this?  for as nobody could ever make such a journey, how can we feel certain that the sun is so excessively hot?  I know that what I say is true for various reasons, but I will only mention one, which is derived from an experiment with the burning glass, that most boys have often tried.


We may use one of those large lenses that are intended for magnifying photographs.  But almost any kind of lens will do, except it be too flat, as those in spectacles generally are.  On a fine sunny day in the summer, you turn the burning glass to the sun, and by holding a piece of paper at the proper distance a bright spot will be obtained (Fig.1).  At that spot there is intense heat, by which a match can be lighted, gunpowder exploded, or the paper itself kindled.

* from Star-Land, being talks with young people about the wonders of the heavens, by Sir Robert Stawell Ball, Royal Astronomer of Ireland, Cassell & Co,1890
("It has long been the custom at the Royal Institution of Great Britain to provide each Christmastide a course of Lectures specially addressed to a juvenile audience")

The virtuous medlar circle

is part of
Anna Tambour and Others

Anna Tambour December 2006