The lighting installations in the former government offices in Tokyo were not perfect, as it wasinstituted when the importance of illuminating engineering had not been generally recognized. Fora long time after the installation, however, it has been nothing improved. The lighting installation ofthe present tcmrorary government offices designed and installed by the Rinji Eizen Kyoku, Department of Finances is quite different from the older one and this paper explains its outlines.

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It is shown that the illuminati-in at any point on a surface illuminated by a surface source of uniformbrightnws bounded by a polygon, which may not have all its sides in one plane, is given by the followingformula; where F denotes the illumination at any point P on the illuminated plane, b the brightness of the surface source, the sum of similar terms for all the sides of the polygon, a the angle subtended at P by a side of the polygon, and 3 the angle which the plane, containing the same side and the point P, makes with the illuminatedplane, and is on that side of the former plane which is away from the surface source.
Then the rectilinear light source is treated as a limiting case, and the following formula is deduced; where E denotes the illumination at any point P on the illuminated plane, Q the candlepower of the rectilinear source in a direction perpendicular to itself, the length of the rectilinear source, p and q the distances from P to the ends of the source, A1 and A3 the angles between the perpendicular to the illuminated plane from any point in thesource, and the perpendiculars to the p and q lines from the same point, a2 the angle subtended at P by the source, 32 the angle between the illuminated plane and the plane containing the point P and the source, andr the length of the segment, between P and the source, of the straight line drawn through P onthe plane containing the source and P, at right angles to the intersection or this and the illuminatedplanes.

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The value of illumination produced by surface sources of any form is obtainable in any directionanywhere in the space.
1. Describe a unit sphere about the point S and a cone with its vertex at S and its base at thesource. Project the curve of intersection of the cone and the unit sphere normal to the tangent plane, T, of the receiving surface at the point. Let its area be SC. he value of illumination is equal to bS'.
When the intrinsic brilliancy, b, is not uniform over the source, divide the source by contours of equalbrightness and get the value of 1 S' for respective zone and sum those values finally.
2. When the intrinsic brilliancy is uniform all over the source, the illuminaton is given by 2dw. cost where dwis the angle subtended at S by the element of the boundary, ois the anglebetween the plane T and the plane decided by that element and the point S and the integration isto be performed along the closed boundary curve.
3. In case of a straight line boundary, o becomes constant for that part of boundary and the contributionof the part is bw.
4. In case of a curved boundary the contribution of that part is When a part of the boundary is of a circular arc, its contribution is given by
5. When the boundary can be considered to be cf the combination of straight lines and circular arcs, we can calculate the value of illumination using the above expressions.
6. Similarly we can obtain the illumination even when the plane T cut the source, so that theproblem dealt with in the previous paper (this journal, vol.8, No.3; Researches of Electrotechnical Laboratory, No.148) is completely generalised.

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The cell-layers of retina of human eye consists of two kinds of cells. The one called“Zapfen” hasa strong visual power and functions in daylight and the other called “Stiibchen” functions in dark andhas about one-fifteenth visual power of the former, Moreover, the former has color sensation butthe latter has not. Man of normal vision in daylight, but of weak visual power in dark has injured“Stiibchen” and is called night-blinder. So, the illuminating engineers must have not only thegood visual power but also good sensation of light.
The sense of deepness (“Tiefenwahrnehmung”) is occured by the single sight of two eyes, the so called“functions of binocular sight.” This function causes a man of latent strabismus the fatigue of eyes (“Latentes Schielen Heterophorie”), but the man of single eye does not feels this fatigue.
The advantages of having two eyes are (1) sharp sense of deepness, (2) wide field of vision and (3) not becoming blindness when injured one eye.
When one eye is good but another is injured, one uses the better one only and his visual poweris never equal to the averaged power of two eyes.

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The search-light mirror has been manufactured strictly respecting the optical efficiency at all events.
In other wovdo, in its manufacturing, the curve of the mirror has been geometricaly measured. Themirror manufacturing companies of the world have attached importance to this point.
Therefore every company has tried many experiments to produce proper articles as a manufacturingfactory for comparatirely long period. It may be said that the ready-made factory cannot producesuch an effectual seach-light mirror. In the 1st and 2nd chapters, I made this fact clear.
For this reason, even in the time of peace there is need of keeping their manufacturing arts.
If the searchlight has no use except for the military purpose, then its continued productionwill be very uneconomical.
In spite of the fact that the manufacturing method belongs to the delicate industry, the manufacturedones ha-ye no use except for military purpose.
Then I discussed, in the 4th chapter, about the nature of the curve of search-light mirror, forthe purpose of explaining whether it is neccessary to set the importance on the only point of elevationof optical efficiency or not, when observed from the point of the nature of the search-lightmirror.
And, as the result of this discussion, I narrated that such a small progress on the optical efficiency of mirror will affect on the luminous efficiency of search-light, and explainnned that the elevation of opticalefficiency in future will has so little effect on the elevation of the luminous efficiency.
On the other hand, I refered to the relation between the absorption of light by air and wave-lengthof light. By this, I ascertained that, if we make the mirror surface that it may have a specialcurve from the point of wave-length of light, we could easily make the variation on luminositywhich could be discerned by the retina, acid by this I concluded that the future progress woulddepend snore on metallic mirror rather than on glass mirror.Then I set the hope for future progress in study of the mauufacturing method of search-lightmirror on metallic one that can illuminate long wave-length light. And as the study of the naethcd, I hope that, though the optical efficiency is dropped to the degree, which has no effect on luminosityin fact, the method that can produce, whenever it is required, even in a most unprepared conditionwithout requiring every-day discipline as the special delicate industry, is the very important problemto study from the stand point of their national economy at peace as to-day.
Secondary I hope that, if the manufacturing method of it beongs to a special delicate industryand if the production of it must be continued in war and peace as continued by all the factory ofthe world, the method which manufacture the mirror that can be used for other purposes whichz 0, nire more delicacy that military purpose, should be studied. We tried to find the method, which answers the above two hopes, in the methods of all thefactory of the world, but in vain. The method showed in the 5 th chapted which has been inventedby me is the only one to answer the above second hope and the method in the 6th chapter is theone to answer the 14 hope.

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