The following article is of special interest when compared with the letter of Mr. Hiram Percy Maxim, published in the Scientific American of September 18th last. Although Mr. Maxim approached the subject from a widely different angle he reached the same conclusions as did Lieut. Zerbee. In justice to Lieut. Zerbee, we wish to explain that the present article was received in March, 1914, long before Mr. Maxim's letter was written, but was mislaid and has only just come to light.