You can download the books from the website only one .tiff image file at a time. (And this is supposed to be a website maintained by the premier institutions of our country. Looks like people no longer take pride in a job well done.)
So, you have the patience to download it. But do you have the patience to actually read these image files one .tiff file at a time?
There are other options like the DLI downloader that help you download the books in PDF format. But I've found that whatever OCR is being used, messes up the text.
I've finally discovered a way to convert these .tiff image files to PDF. Here's how...
It's free for now. So make hay while the sun shines. Go to this website and download Weeny Free Image to PDF Converter, and install it.
Step 1: Open the application and click on Add Images.