On the subject of pneumatic drills, Mr. Bird is emphatic. He says, "no intelligent man puts the slightest confidence in the successful working of any borer, or drill, in the rock of the Hoosac Mountain, unless operated by hand. In a strictly homogeneous rock, machine drills might work, but in a rock like the Hoosac, where the drills, working generally in a comparatively soft material, are liable at any moment to strike veins of quartz, and where a part of the hole will be in the slate and the rest in quartz, no machine drill has yet been found to stand." This reckless and false assertion is made in utter defiance of Mr. Storrow's report and all other authorities upon the Alps Tunnel, which has now been excavated nearly four miles with machine drills on the heading. Mr. Storrow says that masonry is used because the rock "is not homogeneous in character. I stood at the front of the machines, watching them for three quarters of an hour. One drill was driving directly into hard quartz, advancing very slowly, and making the sparks fly at every stroke. Others working in softer spots, were cutting rapidly." Mr. Bird has much to learn about pneumatic drills, and, without going beyond the borders of Massachusetts, he can see a drill operate by compressed air, so indifferent as to the character of the rock it works upon, that it will penetrate the hardest granite and the composite rock of the Hoosac with the same facility, and at a rate which would astonish even M. Sommeiller. The figures upon which Bird bases a "calculation" as to the time of completing the Tunnel, are as far from being correct as his general statements are from the truth. One example is enough to illustrate, and by this the reader may fairly judge what the "calculation" is worth. He says the total length of the Tunnel is 24,586 feet, when the _fact_ is that it is 25,586 feet. This is no mistake of the printer, for the figures repeatedly occur in the pamphlet, and always the same; and it is with this gross blunder that the "calculation" sets out. The truth is that any careful reader of this article, is a Better judge of the whole subject than Mr. Bird, because he will have reliable dates, facts and figures, by the aid of which he can make a calculation for himself, or' form an opinion as to the time within which the work can be done, which will be quite as likely to be correct as any, "I undertake to say," of the oracular Bird.