APPENDIX 179 



in optics it is indispensable, and it may be adapted for demonstrating 

 the thermal properties of radiation. Only delicate manipulators 

 should be allowed to use it, except under supervision. The wooden 

 substitute described in Section 98 will, however, serve for many 

 valuable observations, and will prepare the way for more accurate 

 work. 



PRINTED BY 



SrOTTIS \VOOUE AND CO., NEW-STREET SQUARE 

 LONDON* 



