[The editors are not responsible for S'tatements made in the correspondence column. Anonymous communications cannot be considered, but the names of correspondents will be withheld when so desired.] Wolf's and Brook's Comets To the Editor of the SCIENTIFIC AMERICAN: The following observations of WoWs and Brooks's comets, respectively 1911 a and e. were made on the evening of August 20th, 1911, with the aid of the 40-inch refractor of this observatory. Wolf's comet first observed; very apparent in the 40-inch, and in a rich field. Small. Slight indication of a nuclear condensation. Near a small star. Brooks's comet was observed, first with the 4-inch fnder of the great telescope. The nuclear condensation was a little more apparent than on previous evenings, but the comet was generally about the same. Secondly, with the telescope: The nucleus and matter extending in all directions from it were all that were visible at one time, on account of the size of the feld of view; the former, however, presented a fairly large disk and was nebulous in appearance. The light of the nucleus was practically white. There were several comparatively bright stars in the same feld, which were actually visible through the head of the comet, apparently undergoing no loss in brilliancy whatsoever. The feld itself was very luminous, and in some parts the nebulosity was more apparent than in others, which fact indicated the presence of a tail extending out into space, beyond the head of the comet. FREDERICK C. LEONARD. Yerkes Observatory, Williams Bay, Wis. A Merchant Marine Suggestion To the Editor of the SCIENTIFIC AMERICAN: I wish to express my appreciation of your Merchant Marine number. I have read each of the fve articles twice and fnd them great educators. But I note with sadness that your lay readers, the common people of the United States, upon whom rests the duty of deciding this whole matter, are not taking advantage of your invitation to discuss this problem as it should be discussed. To them I wish to say, The trouble lies with you. Your Congressman is afraid of your vote. Therefore he balks and actually delays the working out of the desty of the greatest nation on earth. It is up to you, you and Bill and John, to get busy and study this problem and make your wishes known. And it is a glorious problem. Try it! To me the fve Merchant Marine articles mentioned have been a means of evolution in my own ic1eas; and in view of the great importance of this problem I am ofering my third letter on the subject,. hoping that you may thus be led to see how easy it is to get into print in a really wortl'y periodical and on a gloriously patriotic subject, and to try it tor yourself. After careful consideration I believe that the following plan would the most effectu'lly pccomplish every desired result and mod evpry worthy objection. In order to get our just share of our commerce with each foreign nation, viz., one-half of it, without the payment of a single dollar in subsidles or the remission of a single dollar in duties, let us negotiate treaties with other nations for an equitable division of the carrying trade between (;ach foreign country and our own, to the exclusion of vessels of all other foreign nations. Thus, taking Brazil as an example, let American vessels loaded at home for Brazilian ports secure Certifcates expressed in fgures based upon the amount of cargo carried multiplied by the number of miles to be traveled. The same vessel, if after unloading in a Brazilian port should reload with a Brazilian cargo for an American port, would receive similar Certifcates from the Brazilian authorities. Both of these Certifcates would then be exchanged for Receipts, the Brazilian government holding the Certifcates and the American ship the Receipts. These papers might be entitled American-Brazilian Merchant Marine Certifcates rnd Receipts. In exactly similar manner Brazilian vessels plying between Brazil and the United States would receive Brazilian-Americ'n Certifcates which would be exchanged with the American authorities for Reeeipts. The American vessel, upon its arrival home, would exchange its American-Brazilian Receipts for Brazilian-American Certifcates, the latter having been obtained by our government as evidence of trafc carried on by Brazilian vessels in exactly the same manner as the Brazilian government obtained American-Brazilian Certifcates. The cancelation of the Receipts received by our government would conclude this part of the process. On the next and succeeding trips the American vessel .would go through exactly the same process except that it would be required to surrender to the Brazilian government Brazilian-American Certificates in amount corresponding to the amount of traffic in which it would be engaging on that trip. O, course, Brazilian vessels would be accorded exactly similar treatment in American ports. Prohibitive duties, then, upon vessels of any other nation than the United States or Brazil and on vessels not presenting the Certificates would keep out all interference and h"ave the carrying trade between the United States and Brazil to be exactly divided between the vessels of the two nations. For no American vessel could profitably engage in the trade unless some Brazilian vessel had ,mgaged in an equal amount of the carrying trade and thus produced the necessary Brazilian-American Certificates. Likewise, Brazilian vessels would depend for their profit upon the existence of American-Brazilian certificates obtainable in their home ports for use in our ports on the succeeding trip. Similar treaties could be made with as many nations as might care to enter into them, and it would certainly not be difficult to find or create sufficient inducements to the ratifying of such treaties by any nations with which we might wish to carry on trade. To me this plan seems so simple and efective and so free from all possible objections as to be worthy of a trial. At any rate I hope you and Bill and John will get to work and see if you can't devise a better plan. Hettinger, N. D. N. J. NOBLE. Rainfall and Parasites To the Editor of the SCIENTIFIC AMERICAN: On page 391, issue of June 24th, you publish an article, “Rainfall and Parasites." I am a veterinarian, with a penchant to investigation of subjects relating to my branches. These parasites require humidity, often ground covered with water, so go through the diferent stages of their complicated life-cycle, is well known and understood. It is unfortunate that careful statistics are not kept in this country regarding the increased loss from this source, and we must refer to European statistics to study this problem. Some years ago Dr. Hutchison, meat inspector at Portland, Oregon, by careful observation found out that cattle and sheep from overfow districts “where carp were numerous, were free from liver fukes (Distornum hepaticum or Fasciola hepatica). The carp is a good scavenger, and destroyed the fukes during their water stage or destroyed the water snails that were the hosts, during a certain period of the Cercariae_ In the nineties I was in practice on the coast of Oregon, in Coos County. There we sufered losses from Distornum lwpaticum, especially after wet seasons, when the bottom lands had been under water and were used as pasture soon afterward. Lungworms also killed many sheep and calves. The life-cycle <-/ flaria pnlmonalis is not known. After many experiments-attempts to cure the :ffected animals-it occurred to me that to p1' cV2nt would be more rational. Clean th'e pastures. How? Ducks, geese. A fock of ducks and geese will go over a good deal of ground, and destroy all iorms of animal life. No douht large tracts could not be “cleaned out” in this manner, but I remember two ranches on which, after two years of systematic running of ducl.s, the calves “emained healthy, and the sheep were free from lungworms. This latter fact was noteworthy, because the life-cycle of this parasite has not been worked out. Some years ago, when at the veterinary department of the University of Pennsylvania, I mentioned these fact,) to Prof. C. F. Marshall, and he fully indorsed my statements, although'he had never had opportunity to put the idea to actual test. The keeping of water fowl, especially ,:ucks, is indicated in game reserves. Ravages of Distornum hepatic1tm among elk, moose, deer, are common, and the ponds are infested before we know the cause and the losses appear. But if some quarters are provided for duckp and swans and geese (they may be ornamental, although Indian runners are best) and their breeding favored, they will destroy many Injurious forms of life that-no doubt about it-are necessary to permit a complete life-cycle of several parasites. This has been worked out in the life-cycle of the fukes (water snails-Cercariae); observations that I made during several years led me to assume that the same means alslO prohibit the development of strongylus flaria and similar parasites (0vis pulmomalis) in sheep and cattle and hogs. Would you ten me flom what paper of Prof. M. G. Moussu your article “Rainfall and Parasites” is a r(sume? At present I am on the staff of the local department of health and sanitation, and am therefore interested in rational prophylactic measures. I always read your valuable publications. Tacoma, Wash. C. H. SCHULTZ, M.D.Y. The Left-hand Mold-board To the Ed ltor of the ScIENTIFIC AMERICAN: In your issue of June 17th a patent office examiner expresses surprise at seeing so many plows in the West with left-hand mold-boards. When I was a boy-I am now sixty-four years old--only the right-hand mold-board was made. In the last thirty or forty years, I have not seen one. The advantage of the left-hand is that the leader walks in the last furrow made, and the off or right-hand horse on the unplowed ground, so both are on solid ground. As the leader is usually the larger, this is very advantageous to the off-horse. With the right-hand mold-board the off-horse had to pull on soft plowed ground. You have probably received many better explanations before this will have reached you. r have had a great deal of interesting and valuable information in the last few years from the SCIE"TIFIC AMERICAN, and am glad to reciprocate in a small way. Taylorsville, Ky. E. D. BOURNE. Niagara Falls fom a New Point of View To the Editor of the SCIENTIFIC AMERICAN: It seems that a great deal of valuable energy is being wasted in hysteria over the supposed wanton destruction of Niagara Falls. We hear great tales of woe, with heavy sob efects, fernint the time when this beautiful cataract shall become a dribble and 1the wild, rugged gorge shall be but a dirty, grinding workshop where a coterie e millionaires are enabled to pile up further hoards o unearned increment, to the detriment of all “the people." I hold that whole volumes of this kind of gush can be very easily dispensed with or turned into other channels, without any injury to the body politic. It seems strange to me that in all this discussion, we hear nothing whatever of the good to come to humanity from allowing this immense falls to work out its board and -lodging. Here we have a force of a sum total of 5,000,000 horse-power not doing or2 ·thing but tumbling down stairs and showing of its shape (the latter being at present in bad order and geting worse). But a very small part of this immense power is put to work to beneft man, while under proper management, 'ully two-thirds of it could be made available and the falls sitill left a thing of beauty and a joy forever. The works now using the water seem to have their outfalls on a very high level. Were these at a lower level, far less water would do the same work. Then look at the way the falls itself is wasting good material; there is that ugly Y-shaped crotch in the “horseshoe,” where the water is now about twenty feelt deep. Some aesthetic asses becom, veTY emotional over this fault, referring to it as the “great green heart.” It reminds me more of a stomach, greedy and insatiable and bidding fair to soon ruin the whole show by eating hack into the rock and forming a narrow sluice. To this feature, more than the power houses, can be attributed the shallowness of water on the other parts. My remedy is this: let the State of New York and the Province of Ontario jointly build large sluiee-ways around the falls, their combined capacity great enough to accommodate all the water running over the falls. By diverting the water to them, ,the edge of the falls can be built up of concrete and trimmed of to a uniform level, so that onethird of the water would at all times keep the falls falling. If thought necessary the coping could be made of vanadium steel, so as to insure against any wearing away of the bed and spoiling it. This would allow of an immense amount of energy to be available which would give employment to many people and furnish necessaries of life to thousands at cheaper prices than if made by using coal and that without smutting up the country with smoke. In addition it would bring a good revenue to the State from the renting of water supply, and it wouldn't be any more difcult than for Ithe Panama Canal engineers to take care of the Chagres Riv8r. or the Dutch engineers to keep out the Atlantic Ocean, or for the Dublin police to keep the loyal Irish from setting Ireland free. A strong, husky man looks far bebter when engaged in honest toil, making the world better for his existence, than when he is standing around a street corner showing of his shape, and I say the same of a waterfall. Washington, D. C. SENEX SMITH.