Intelligence and Miscellaneous Articles. 223 



thus determined as a new origin, and substitute in the n (trans- 

 formed) equations for one of the variables x a series of values 

 + B, + 2^, &c. Corresponding to each of these substitutions we have 

 n equations for y. For each of these systems determine the Median 

 according to Laplace's Method of Situation. This series of Medians 

 forms one locus for the sought point. A second locus is found by 

 transposing x and y in the directions just given. The intersection 

 of these loci is the required point. 



The method may be extended to any number of variables. Tor 

 example, in the case of four variables, x, y, z, w, we should con- 

 struct one table containing the Median values of w corresponding 

 to each triplet of values assigned to x, y, z ; and three similar tables 

 for the Median values of x, y, z, respectively. The system of values 

 for x, y, z, w, which is identical in all the tables, forms the required 

 solution. 



The advantages claimed for the new method are that, while in 

 the typical case of the laws of facility being all Probability Curves, 

 the generalized Method of Situation is only slightly less accurate, 

 and is considerably less laborious, than the Method of Least Squares; 

 in the abnormal case of Discordant Observations the proposed 

 method is not only more convenient, but better. 



It is much to be wished that some practical astronomer would 

 give this method a trial by employing it in some laborious and 

 important calculation. F. Y. Edgewokth, 



Kings College, London. 



A NEW PHOTOGRAPHIC SPECTROSCOPE. BY C. C. HUTCHINS. 



The constant demands of spectrum analysis for ever increasing 

 accuracy can be satisfied only by instruments of the highest dis- 

 persion and most perfect defining-powers ; and when applied to 

 photography the dispersion must be produced directly, and not by 

 enlarging lenses at the camera. The large apparatus of Rowland 

 does this most beautifully, as the writer, who has used it for the 

 past year, can testify ; but the fact that a large room must be set 

 aside for its accommodation, and moreover that the large concave 

 gratings are very difficult to obtain, will forbid its use to most 

 workers. 



I have therefore devised the following simple and, it would seem 

 upon short trial, effective arrangement for producing the desired 

 results : — 



A rather long slit is placed at the focus of a crown-glass (or, 

 better, quartz) lens of 40-feet focus. The ray from the slit, after 

 passing through the lens, falls upon a large flat grating, mounted 

 to turn about an axis passing through the middle line of the ruled 

 surface. The spectrum is projected by the same lens upon a hori- 

 zontal arc of 40-feet radius, and is observed a. little to one side or 

 above the slit. The spectrum will not be normal throughout its 

 length unless the radius of projection be kept constant. I think 

 this had better be provided for by employing two lenses of crown- 

 glass, the one nearer the grating fixed, the other movable, than by 



