ments described, which merely enables non-professional persons to make a record of certain selections and place them on paper, where they can then be submitted to a surgical expert who can as well decide upon that evidence as though he were present at the examination, with the understanding that all suspicious cases are to be examined by him in person.

What is gained by this? The expense under the law passed in Massachusetts and Connecticut was estimated to be from two to three dollars per man, to be paid by the roads, and with a penalty for the employment of any man not provided with the certificate of an expert appointed by the Governor of the state. For this sum, say three hundred dollars per one hundred men, the road could be informed that ten to fifteen employés were unfit for its service; no provision having been made for the correction, by glasses or other treatment, of the trained men, otherwise so valuable, and no time being allowed to replace men especially fitted for certain duties; and the roads were to be thus taxed for the more than decimation of their entire force, whilst the employés were subjected to a pitiless scrutiny that would end in the summary dismissal of about fifteen per cent from the discharge of duties for which they had spent perhaps years of training. It can easily be understood why such a law would be resisted by all the political or other influences of the entire railway force in a state, from the directors and presidents to the lowest employés, and should awaken also the opposition of the holders of its securities.

By the system adopted on the Pennsylvania Railroad, the men below the standard are detected unerringly by their own officials; those color-blind are sent to the surgical expert and after his decision, are yet retained in the service where possible, being placed where their defects can work no harm. Any valuable man below the standard of visual power can be sent for treatment, if the officers so decide, or the men can elect to have their cases treated elsewhere upon the condition that they can pass the proper examination afterwards. The one plan, it is evident, is expensive, irritating to the whole personnel and disorganizing; while the other is economical, confidential and orderly. By a wise liberality in aiding men to have their acuteness increased by proper glasses the officers of the road have been able to carry out their wishes without any noticeable opposition from the employés, and have thus effected

for hundreds what would otherwise have cost them thousands of dollars, if any plan hitherto proposed had been adopted. Since Only the color-blind and those needing surgical skill have been sent to the expert, he has not been in a position to give statistical tables of the examinations, and he therefore submits the following letter from Mr. Charles E. Pugh, the general manager, to substantiate his statements and bear witness to the success of the entire system.

DR. WM. THOMSON,

PENNSYLVANIA RAILROAD Co. Office of the General Manager, 233 So. 4th St., Philadelphia, Pa., April 26, 1884.

Surgical Expert, Penn. R. R. Co.,

1426 Walnut Street, Philadelphia.

Dear Sir: The practical examination of our employés as to their acuteness of vision, color-sense and hearing, in accordance with the system proposed to us by you and carried out under your supervision, has been extended to all the various divisions of the Penn. Railroad, has embraced nearly all of the men engaged in duties requiring the use of signals now in the service and will be used hereafter in the selection of men placed on such duty, or in the employment of new men entering our service.

In approaching the completion of the task of examining those now in our service (more than twelve thousand employés having now been submitted to your system), I desire to express to you our entire satisfaction with the rules and regulations, tests and instructions prepared by you, as well as with the personal supervision instruction of examiners, and examinations and decisions upon doubtful cases and persons referred to you for final action.

Our division superintendents and their staff officers have been able to deal promptly with the great majority of defective men and thus avoid the necessity of availing themselves of that clause in the instructions which provides for an expert examination in each suspected case, and have in this way carried out your purpose without undue excitement among the men, in a speedy and confidential way, and with economy to the company. The proportion of those defective in color-sense, vision and hearing was found by the examination of two thousand men before the adoption of this plan to be 4 per cent of the first and about 10 per cent of the latter, and I am satisfied from my reports that all those thus deficient are being relieved of duties which they cannot perform, and that the great dangers to the public and to the other employés of loss of life, and to the company of possible destruction of property, have been averted, so far as their defects are concerned.

I am frequently asked by prominent officers of other railways and government officials to give an opinion as to the practical usefulness of our

system of examination, and it affords me much pleasure to emphatically commend it in all its details; and I feel that we have good reason to be satisfied with this the first successful attempt to bring the entire body of men engaged in signalling upon a railway in our country, under control by the practical application of scientific facts. Having eliminated these dangerous persons from our present force we propose to keep it free from them in the future by a steady application of our present system.

Yours truly,

CHAS. E. PUGII,

General Manager.

To this great corporation, extending through six states, operating five thousand miles of track, with nearly if not quite fifty thousand employés, and responsible for the lives of millions of people each year, must be accorded the honor of having been the first to obtain the desired control of the visual defects of their men by a wise and intelligent application of scientific laws.

Their example has been extensively followed elsewhere and their instrument has been obtained by more than thirty other roads from the manufacturer. It has also been ordered by "The Board of Trade of England," by many distinguished medical men abroad, and has recently been, with the entire system, adopted and will no doubt, be put into operation by a director of the Southwestern Road in England. There is no longer any reason why losses of life and property should occur in railway service from visual defects; and an enlightened public opinion should now insist upon the adoption of some similar plan upon the hundred thousand other miles of railway now being operated in our country.

Having been placed as the American representative on the committee on Control of Vision at the International Congress in London three years ago, I have urged upon the Naval Committee of our Congress the value of this large experiment with a view to have a law passed to form an International Commission to establish a uniform system of signals, examinations, etc., both on the land and on the water. There is no doubt that accidents must occur on the sea, and the recent loss of the Tallapoosa has not only been ascribed to a wrong interpretation of the colored signals, but the commission appointed to investigate the accident have been especially directed to examine for color-blindness the lookouts on the ships.

NOTES ON ANEROIDS. By Prof. M. W. HARRINGTON, University

of Michigan, Ann Arbor, Mich.

[ABSTRACT.]

1. The popularization of the barometer.

This can best be done with the aneroid; fairly accurate ones should be retailed at a low price.

2. Improvements of the aneroid for accurate measurements. The three or four recent German modifications are briefly described and discussed.

AN ABSOLUTE SENSITOMETER. By Prof. G. W. HOUGH, Director Dearborn Observatory, Chicago, Ill.

[ABSTRACT.]

VARIOUS methods have been employed for ascertaining the sensitiveness of photographic plates, but we do not know that any hitherto used are capable of giving directly the sensitiveness as referred to any convenient standard. The use of blackened gelatine films may give sufficiently reliable results, but from the nature of their construction, no two instruments will be precisely alike, and even in the same instrument there is no definite relation between the different parts of the scale.

The use of a series of tubes having unequal areas might answer under certain conditions, but such an apparatus would be complicated.

It occurred to me that if a perforated disk was made to revolve in front of a scale of numbers, the light received by each would be directly proportional to the angular opening in the disk. To illustrate, suppose we have a semicircular disk, which is made to revolve rapidly, then any number covered by it when in rotation would receive only one-half as much light as one outside of its circumference. If the disk revolves with sufficient speed both numbers will be constantly visible to the eye, but one will receive only one-half as much light as the other. On this principle is based the sensitometer about to be described.

Let any scale of numbers from 0 to 100 be photographed or painted on clear glass or the numbers may be engraved on a black

ened glass plate. The plate to be tested may then be placed behind it, to make a contact negative. In front of the scale, the snail or perforated disk may be rotated so as to give each number its proper amount of illumination, the light being a standard candle at one foot distance.

If the time of exposure be one second, and the last number visible in the negative is two, the equivalent exposure will be

If another plate under the same condition shows the number 4 in the negative, its equivalent exposure will be second. The reciprocal of these fractions will be the direct measure of sensitiveness.

In other words, the apparatus will give the actual time required for the light of one standard candle at one foot distance to make a legible record, and this time is the standard of sensitiveness; the only source of error will be in the standard candle.

In testing rapid emulsion plates, it is desirable to place the standard candle at eight or ten feet distance, in order that the error in making the exposure may be reduced to a minimum.

AN EXPERIMENT FOR ILLUSTRATING THE CONVERSION OF MECHANICAL ENERGY INTO HEAT. By Prof. CHAS. E. MUNROE, U. S. Naval Academy, Annapolis, Md.

[ABSTRACT]

On

A PERFORATED cork having been attached to the arbor of a Griscom electro-motor, a test tube is inserted in the cork. A wad of gun cotton is placed in the test tube and the tube corked. setting the motor in revolution, sufficient heat is generated to fire the gun cotton and blow the cork from the tube.

ON THE VARIATION OF THE RESISTANCE OF CARBON UNDER PRESSURE. By Prof. T. C. MENDENHALL, Ohio State University, Columbus, Ohio.

[ABSTRACT.]

THE variation of the resistance of carbon under varying pressures has been made the subject of investigation by a number of phy