Copper spherical burning mirror <a href="https://en.wikipedia.org/wiki/Ehrenfried_Walther_von_Tschirnhaus" class="extiw" title="en:Ehrenfried Walther von Tschirnhaus">Ehrenfried Walther von Tschirnhaus</a>, Kieslingswalde, 1686.
<p>Height = 230,0 cm, Diameter = 158,5, Focal distance = 113,0 cm; Thickness mirror ca. 2,0 cm 
</p>
Mathematisch-Physikalischer Salon, B V 10
<a href="//commons.wikimedia.org/wiki/User:Ad_Meskens" title="User:Ad Meskens">Ad Meskens</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>