Early Telegraph Insulators?
Or 20th Century Tree Insulators?

Generally recognized as 1850's era telegraph insulators, glass blocks continued to be advertised in supply catalogs well into the 20th Century. Did insulator companies like Brookfield continue to make them, or were they trying to market their unsold stock?                                 
                                                                                                        

Brookfield sold glass blocks as tree insulators. The advertisement on the left is from a 1912 Brookfield catalogue. That catalog is reproduced in a book by Henry Morgan Brookfield. His book is advertised on page 57 of this issue of Crown Jewels.