158 



SCIENCE. 



[Vol. XI. No. 269 



used, — one that is durable, and not liable to get out of order ; 

 which will fix the objective firmly in position, and yet will permit it 

 to be attached or removed with the least possible expenditure of 

 time and energy. It must be admitted that the screw meets all 

 these requirements except in the important matter of attaching and 

 removing the objective. The screw is not an expeditious mode of 

 attachment, although it may be improved by lessening the number 

 of the threads so that only one or two turns of the objective tube 

 would be needed in order to bring it to position. Most objects 

 require to be studied under different amplifications, and the time 

 spent in changing from one to another is a real loss. Most work- 

 ing microscopists will begrudge every second spent in changing, 

 not only because their time is valuable, but also because an object 

 may thus be lost, at least for a time, especially if it is a moving 

 object. If it is possible, objectives should be attachable and 

 removable without having to draw back the tube of the microscope 

 or disturb the object. This is accomplished by the revolving nose- 

 piece, but under the disadvantage of being somewhat bulky ; also it 

 answers for only two or three powers, and leaves the unused ob- 

 jectives exposed to the dust. The Facility nose-piece, the Zent- 

 mayer cut-away nose-piece, etc., show that objectives can be at- 

 tached more quickly than by the ordinary screw ; yet, like the 

 screw, these devices require drawing back the tube in order to be 

 attached. It will be a great gain if some way can be devised 

 whereby each objective can be easily and instantly slid into place 

 from the side, the new objective pushing out the one in former 

 use as it is itself pushed in. This would probably involve a square 

 or rectangular plate fixed to the top of the objective, sliding in ways 

 fixed to the instrument tube, or some other equivalent arrange- 

 ment. It is not, however, my present purpose to discuss the ways 

 and means for gaining the important end of attaching the objec- 

 tive by some more speedy device than the screw, only to call 

 attention to the subject. If no device superior to the screw can 

 be found, by all means, let the fittest survive. On the other 

 hand, it is neither mechanical, nor in the end economical, to let 

 the screw, because it is already in the field, stand in the way of 

 a better device. At the present time both microscopists and manu- 

 facturers are agreed on the society screw, and those who prefer 

 nose-pieces have to go to the expense of providing adapters. It 

 will be no more than fair to change the programme. Suppose we 

 agree on some standard form and size of nose-piece, and let those 

 who prefer screws provide the adapters. 



By having the nose-piece attached directly to the objective tube, 

 we would do away with screws entirely, also all need of adapters 

 except to tubes already provided with screws. 



It may be objected that there are so many possible ways of at- 

 taching objectives, that there is no probability of coming to an 

 ■ agreement upon a single standard size and form of attachment 

 whereby the objectives of all makers could be used on every 

 microscope, as they are under the present arrangement of the 

 society screw. 



In reply it may be said that we cannot know this until after the 

 attempt has been made. If American microscopists take con- 

 certed action for making their needs known, it must result in a 

 great many suggestions as to the proper mechanical devices for 

 securing the desired ends. The resources of mechanicians were 

 not exhausted when the screw was invented. I believe it is only a 

 question of time when the ordinary screw will be replaced by some 

 more expeditious device, perhaps by some form of sliding collar, or, 

 if the term be preferred, by the American nose-piece. 



G. H. Stone. 



Colorado Springs, Col., March i6. 



Is the Rainfall increasing on the Plains ? 

 In your issue of March 2, I observe the statement attributed to 

 the chief signal officer, corroborating " the prevalent opinion that 

 the rainfall in the West is increasing," while Mr. Henry Gannett 

 '• dismisses this popular idea as baseless." My own opinion is de- 

 cidedly in favor of the affirmative of this question. My personal 

 observations for twenty years at this point indicate the existence of 

 a rainfall cycle of about seven years in duration, each septennial 

 period including two or more consecutive years of precipitation 

 above the average, and a similar series of years with precipitation 



below the average. A seven-year cycle is also illustrated in the 

 Fort Leavenworth rainfall, whose records cover double the period 

 of my own observations at Lawrence. Recognizing the existence 

 of this cycle, it will require a minimum series of fourteen years of 

 records to warrant a division of the period into two equal parts for 

 the purpose of determining the question of an increase of rainfall. 

 I would therefore eliminate from Mr. Gannett's list all but nine of 

 the twenty-six stations. At these stations the aggregate increase 

 of precipitation in the second half of the periods of observation is 

 109 inches, which gives an average annual increase of 1.28 inches 

 for the nine stations. This is certainly a decided increase, although 

 the average period of observation is only nineteen years. 



But the length of the period of observation at Fort Leavenworth 

 is thirty-nine (instead of twenty-eight, as given in Mr. Gannett's 

 table), — from 1836 to 1874. A study of this series of observation 

 is of great interest, since it is the largest series in our possession, 

 and especially since its division into two equal parts throws the first 

 half entirely into the period preceding the settlement of Kansas, while 

 the second half is placed entirely within the period of settlement of 

 this great Commonwealth. The total precipitation in the first half of 

 this period (ending June 30, 1855) was 592.84 inches, giving an annual 

 average of 30.40 inches, while in the second half (ending Dec. 31, 

 1874) it was 696.29 inches, giving an annual average of 35.70 inches. 

 This shows a total increase of 103.45 inches, or an average annual 

 increase of 5.30 inches. This is assuredly a change worthy of 

 notice, involving an increased precipitation of more than seventeen 

 per cent. 



My figures concerning the Fort Leavenworth rainfall are derived 

 from a transcript of the records furnished by Prof. Joseph Henry 

 of the Smithsonian Institution, and published in the ' Annual Re- 

 port of the Kansas Board of Agriculture for the Year 1874.' In 

 this transcript there are no records for 19 of the 468 months of the 

 39 years. Five of these blanks occur in the first half of the period, 

 and have been filled by inserting the average precipitation for the 

 months in question. Twelve of the blanks occur in the second half 

 of the period, and have been filled by inserting the actual rainfall 

 for those months at Lawrence, Manhattan, and Fort Riley, all of 

 which stations are within about one hundred miles of Fort Leaven- 

 worth, and have a smaller rainfall than that of Fort Leavenworth. 



The following diagram is appended as exhibiting more clearly this 

 periodicity according to my observations at Lawrence : — 











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ANNUAL RAINFALL . 



VRENCE, KAN., 



A similar platting of the Fort Leavenworth rainfall exhibits six 

 periods of excessive precipitation, separated by intervals of seven 

 years, and alternating with periods of deficient precipitation, in the 

 same manner as in the above diagram of the Lawrence rainfall. 



F. H. Snow. 



Lawrence, Kan., March 13. 



Bacteriology in our Medical Schools. 



In connection with the subject of bacteriology in the schools, it 

 should be stated that Johns Hopkins University, though it has not 

 yet established a medical course, has organized a pathological in- 

 stitute. In this institute the subject of bacteriology is thoroughly 

 taught in the most approved manner by a competent board of in- 

 structors. H. W, Conn. 



Middletown, Conn., March 21. 



