we Description of a Burning Mirror. 
whatever side the point I is, in whatever position it is with 
respect to the solar ray, this ray will be reflected on the same 
side by the plain mirror.”” Butinflammation does not take 
place by means of burning mirrors, unless when several 
rays are collected in one and the same place, and when the 
heat is condensed to the burning point. It is thus that, 
when a fire is kindled in any place, the parts adjacent and 
the circumambient air receive a proportionate degree of 
heat. If, therefore, we. conceive that on the contrary all 
these degrees of heat are collected and concentrated at 
this place, they will there exert the force of the fire just 
mentioned. Let us, therefore, bring and collect at the 
point P removed from the point A the distance which we 
have assigned to it, other different rays, by means of 
plain and similar mirrors, in such a manner that all these 
ravs, united after reflection, may produce inflammation: 
this may be effected by means of several persons holding 
mirrors, which, according to the position indicated, send 
the rays to the point l’...... 
“* But in order to avoid the embarrassment resulting from 
intrusting this operation to several persons, for we shall 
find that the matter intended to beburnt does not require 
less than 24 reflections, the following construction must 
be followed: | 
“© Let ABPAEZ be the hexagonal plain mirror, and other 
adjoining similar mirrors, and attached to the first accord- 
ing to the straight lines AB, BP, TA, AE, EZ, &c. (fig.6), by 
the smallest diameter, so that they may be moved on these 
lines, by means of plates or bands applied, which unite 
them to each other, or by means of what are called hinges. 
If, therefore, we bring the surrounding mirrors into the 
same plane with the mirror in the centre, it is clear that all 
the rays will undergo a reflection similar and conform to 
the common position of all the parts of the instrument. 
But if, the ceutre mirror remaining as it were immoveable, 
we dexterously incline upon it all the other mirrors which 
surround it, itis evideut that the rays reflected by them 
will tend towards the middle of the place where the first 
mirror is directed. Repeat the same operation, and around 
the mirrors already described, placing other similar mirrors, 
all of which may be inclined’ towards the central mirror, 
collect towards the same point the rays which they send, 
so that all these united rays may excité inflammation in the 
given spot. 
** But this inflammation will take place better if you can 
employ.for this purpose four or five of these burning mir- 
rors, 
