CH. XXIX.] THE SPECTROSCOPE 467 



between the D and E lines ; haemoglobin gives only one ; and other 

 red solutions, though to the naked eye similar to oxyhaemoglobin, will 

 give characteristic bands in other positions. 



A convenient form of small spectroscope is the direct vision 

 spectroscope, in which, by an arrangement of alternating prisms of 



FIG. 332. Diagram of Spectroscope. 



crown and flint glass, the spectrum is observed by the eye in the 

 same line as the tube furnished with the slit indeed, slit and prisms 

 are both contained in the same tube. 



In the examination of the spectrum of small coloured objects a 

 combination of the microscope and direct vision spectroscope, called the 

 micro-spectroscope, is used. 



The next figure (fig. 333) illustrates a method of representing 

 absorption spectra diagrammatically. The solution was examined 

 in a layer 1 centimetre thick. The base-line has on it at the proper 

 distances the chief Frauenhofer lines, and along the right-hand edges 

 are percentages of the amount of oxyhaemoglobin present in I, of 

 haemoglobin in II. The width of the shadings at each level repre- 

 sents the position and amount of absorption corresponding to the 

 percentages. 



The characteristic spectrum of oxyhaemoglobin, as it actually 

 appears through the spectroscope, is seen in the accompanying 

 coloured plate (spectrum 2). There are two distinct absorption 

 bands between the D and E lines; the one nearest to D (the a 

 band) is narrower, darker, and has better-defined edges than the 

 other (the /3 band). As will be seen on looking at fig. 333, a solution 

 of oxyhaemoglobin of concentration greater than 0*65 per cent, and 

 less than 0'85 per cent, (examined in a cell of the usual thickness of 

 1 centimetre) gives one thick band overlapping both D aijd E, and a 

 stronger solution only lets the red light through between C and D. 

 A solution which gives the two characteristic bands must therefore be 

 a dilute one. The one band (y band) of haemoglobin (spectrum 3) is 



