Early divided back postcard of Boylston station, postmarked 1919. This was a "hold to light" type, where the windows of the image were a thinner paper designed to be translucent.
Unknown author<span style="display: none;">Unknown author</span>
Scanned postcard from eBay auction: "<a rel="nofollow" class="external text" href="https://www.ebay.com/itm/1910-Hold-to-Light-Tremont-St-Common-Subway-Station-Boston-MA-postcard-Koehler/233484023472">1910 Hold to Light Tremont St Common &amp; Subway Station Boston MA postcard Koehler</a>"