In the middle of creating a book in Aperture I need more photos. How can I add them to the browser at this stage?
You can add more images to your book, by dragging them from the browser to your book album. Switch to the Library Inspector, select the album or project with the images in the source list, and then drag these images onto the book icon. That will add them to the book album, and then double click the book album again to continue working with the book.
In additon to what Léonie wrote Aperture is modeless, that is it will remember wat you were doing in one area of the program if you leave that area nd do somehting else in another area.
So you're not locked into finishing your book once you start. You can work on the book and then leae it and do work in other projects and then come back to the book. Aperture will remember where you were.
So if you need more images in a book or you want to import other images to use in the book you can leave the book do those things and go back to it.
Also, don't forget you are not actually copying images to the book. A book is just a special kind of album. Albums only have pointers to the images which are in projects. The reason I mention this is that if you add an image to a book and then sometime later edit that same version of the image in its project, the change will appear in the book the next time you open it. (e.g. add a color image to a book page, then change it to a BW image in its project, it will change to BW in the book also). To avoid this you'd need to make a new version just for the book.