January 13, 1888.] 



SCIENCE 



than by the first method. If he should go still further, and ob- 

 ject to calling a day foul unless at least .05 of an inch of rain fell, 

 and proceed to verify the above predictions accordingly, the per- 

 centage of success would rapidly approach zero. By disregarding 

 this evident truth. Prof. H. A. Hazen has, in his letter on p. 322 of 

 the last volume of Science, involved himself apparently in great 

 confusion. 



Mr. Rotch and the writer have during the last year published 

 statements showing that local predictions issued from the Blue Hill 

 Observatory for longer periods in advance than those issued by the 

 Signal Service for this vicinity have had a higher percentage of suc- 

 cess than the predictions of the latter. Some of these statements 

 were copied in the notes of foreign meteorological journals, and 

 were prominently referred to in an article by Dr. Klein. 



In September, 1887, letters were received from Professor Hazen 

 in which he referred to these statements, and said that our sup- 

 posed higher success was ' all moonshine,' and was entirely due to 

 our methods of verification. Moreover, he said it was unfair to 

 verify predictions made for Massachusetts by the Boston record 

 alone, and proposed that he and the writer should try together pre- 

 dicting for Boston alone. This seemed eminently fair, and the 

 writer agreed to it ; but, to make sure that both had a clear under- 

 standing of the meaning of the terms to be used, definitions of the 

 terms 'fair weather,' etc., used by the writer in making predictions, 

 published by the Associated Press of southern New England, were 

 sent to Professor Hazen. He materially modified these, and sent 

 the following definitions and rules. The temperature rules are omit- 

 ted. 



Plan for Weather and Temperature Predictions and 

 Verifications at , Boston and Washington (all 

 verifications to depend on the observations [taken 

 tri-daily at boston]; predictions to be made at or 



before 2 P.M., TO HOLD FROM MIDNIGHT TO MIDNIGHT). 



Prediction : Fair Weather. — Successful : if fair three times ; 

 cloudy, fair, clear in any order ; and any cloudiness less. Failure : 

 if cloudy twice in any order ; cloudy, fair, fair in any order, and any 

 cloudiness above ; a drop of rain. 



Prediction : Threateiiing. — Success : if cloudy twice in any 

 order; cloudy, fair, fair and any cloudiness above; rain .01 or less. 

 Failure : if fair three times ; cloudy, fair, clear in any order ; and 

 any cloudiness less; rain over .01. 



Prediction: Rain. — Success: rain at anytime over .01. Fail- 

 ure : rain .01 or less and any cloudiness. 



Predictions were begun according to these rules, and the writer 

 sent Professor Hazen a prediction during each day in October ex- 

 cept on Sundays. Professor Hazen has correctly given these pre- 

 dictions, with the corresponding weather at Boston, on p. 323 of the 

 last volume of Science. If any one will take these tables, and care- 

 fully verify the predictions in accordance with the above rules, he 

 will find that sixteen of the predictions in Column i, which repre- 

 sent the Blue Hill predictions, were verified, that is, sixty-four per 

 cent of the whole ; while only twelve of No. 2 (Professor Hazen's) 

 were verified, or forty-eight per cent of the v/hole. This excess of 

 sixteen per cent for Blue Hill apparently did not suit Professor 

 Hazen, and he proceeds to obtain from Professors Russell and Up- 

 ton other definitions and rules for verifying fair, threatening, and 

 rainy weather ; and, finding that these give a higher per cent for 

 No. 2, he omits entirely to give his own rules. The writer likes 

 Professor Upton's scheme better than that of Professor Hazen, only 

 his predictions were not made in accordance with such a scheme. 

 The predictions sent to Professor Hazen were not made to be veri- 

 fied in detail, but only to agree with his rules ; and it so happened, 

 that, while the writer was predicting with Professor Hazen, he was 

 also predicting for the Boston papers ; and when he predicted in 

 these, " rain followed by fair weather," or vice versa, he merely 

 wrote on Professor Hazen's card " rain," because, according to 

 Professor Hazen's rules, any rain of over .01 of an inch was to be 

 accounted success. Hence it is seen to be manifestly unfair to 

 verify them by other rules. 



According to the definitions sent to voluntary observers by the 

 Signal Office, a fair day is one on which less than .01 of an mch of 

 rain or snow (melted) fell, while a foul day is one on which .01 of 



an inch or more fell ; and the writer was recently told by one of the 

 predicting officers of the Signal Service that this was virtually the 

 method used in the official verifications. 



At Blue Hill this definition has been adopted, and hence the pre- 

 dictions are exactly comparable with those of the Signal Service. 

 For October the Blue Hill predictions thus verified gave a percent- 

 age of success of eighty-five, while the Signal Service predictions 

 only gave fifty-eight per cent for this vicinity. In both cases Sun- 

 days were omitted. Professor Hazen knew how this percentage 

 was obtained, and yet in his letter to Science he writes as if it 

 were a surprising thing that the same predictions should give 

 eighty-five per cent when two things were considered, and only 

 sixty-four per cent when three things were considered, in the veri- 

 fication. H. Helm Clayton. 



Blue Hill Observatory, Jan. 4. 



American Microscopes. 



In my letter to Science (x. No. 252) in regard to American mi- 

 croscopes, I stated that my opinion in regard to them was based 

 upon the examination of those brought to me by students. I hoped 

 thus to avoid the appearance of claiming to have made an exhaus- 

 tive examination of all forms of American microscopes. I regret 

 that I did not make an express disclaimer. 



Dr. Prudden has placed me under obligation by his very cour- 

 teous letter in Science ol Dec. 23, which calls attention to Grunow's 

 new stands. Dr. Prudden's surmise that I was unaware of Gru- 

 now's recent work is correct. It is with much pleasure that I now 

 learn that he is endeavoring to meet so admirably the demands of 

 professional biologists and the needs of students. 



Mr. Edward Bausch considers me unjust, if I do not misinterpret 

 his letter {Science, Dec. 23). He appears to me to have overlooked 

 that I wrote only in regard to microscopes suitable for biological, 

 and particularly histological work. I have heard that the elaborate 

 American stands were favorites with amateurs, but in regard to 

 that point I expressed no opinion. I believe, however, that the in- 

 creased demand for what is known as the continental stand is due 

 to the rapid growth in numbers of those who use the microscope as 

 a professional instrument, and to the extensive introduction of lab- 

 oratory work in histology as a part of the course of instruction in 

 our colleges and medical schools. 



In regard to the Harvard microscopy Mr. Bausch may recollect, 

 that, when he first came to consult me, I then urged upon him the 

 advisability of frankly imitating one of the Zeiss stands. This ad- 

 vice he decided not to follow. At the time of his second visit I 

 think that I again expressed to him the same advice. I also coun- 

 selled him to make certain essential and some minor alterations. 

 He made all of the latter, none of the former, if my memory is cor- 

 rect. He subsequently sent me a stand and two objectives to test. 

 In reply I wrote the opinion which he has quoted in his letter, and 

 which I see no occasion to alter now, but am compelled to append 

 a remark for my own justification. The remark is, that I have 

 since then examined a number of the Harvard microscopes brought 

 to me by students. The stands have been of fairly good workman- 

 ship, but the objectives I have found, by conscientious examination, 

 to be not infrequently of inferior quality, and most decidedly not 

 satisfactory. As far, therefore, as my experience enables me to 

 judge, I still feel disinclined to bestow the commendation upon these 

 special American microscopes which I am ready to give to some of 

 their foreign competitors. 



My letter was not intended to impugn the honesty of the Ameri- 

 can manufacturers of microscopes, and I do not wish to do so at 

 all. I do wish to call attention to the fact that their policy has been 

 to supply instruments, which, however suitable for certain persons, 

 are not as satisfactory for the work of the professional biologist, 

 the medical practitioner, and of students, as are certain of the 

 European microscopes. 



It is to be hoped that Professor Ryder's interesting letter will 

 bring about the result he suggests, of having a competent commit- 

 tee take up the consideration of the best attainable microscope. 

 For my own part, I feel much pleased with a German stand of 

 quite new model, which I purchased last summer. After using it 

 a good deal, I have little change to wish for in it. If it should please 

 others equally, it may be considered to represent an advance towards. 



